Constant time delay to teach reading to students with intellectual disability and autism: a review

Abstract

The ability to read promotes academic success and serves as an essential prerequisite skill for many postsecondary opportunities. However, developing proficient reading skills is particularly difficult for many individuals with intellectual disability (ID) and autism spectrum disorder (ASD). Reading is an important life skill for all individuals, and it is essential for reading instruction to be grounded in research to achieve optimal learning outcomes. We conducted a review of the literature covering a 15-year period (2005–2020) to examine research measuring the effects of an evidence-based practice, constant time delay (CTD), when used as a reading intervention to teach participants with ID and/or ASD. Studies evaluated the acquisition of functional or academic reading skills across two instructional delivery methods: teacher-delivered and technology-based CTD. All reviewed research used a single case research design to experimentally validate the effects of CTD as a reading intervention, and findings across studies revealed a functional relationship between variables. That is, when applied as a reading intervention, CTD led to acquisition of academic or functional reading skills in participants with ID and/or ASD regardless of delivery method. Recommendations for research and practical application of CTD when teaching reading are provided.

Reading instruction is a central component of educational programing. However, students with intellectual disability (ID) and autism spectrum disorder (ASD) face cognitive barriers that may inhibit their ability to keep up with the pace and high demands of typical reading instruction (Aldosiry 2020, Browder et al. 2006). Consequently, reading deficits are prevalent among students with ID and ASD (Hendren et al. 2018, Katims 2001). Katims (2001) found that nearly 80% of children identified with ID in the mild or moderate range display minimal reading abilities. It has been suggested that deficits in working, short- and long-term memory may contribute to the acquisition and maintenance of literacy skills for individuals with ID (Cohen et al. 2008, Coleman et al. 2012). Students who struggle to develop proficient literacy skills face other academic hardships and may be less autonomous later in life (Browder et al. 2009, Knight et al. 2003). For that reason, it is critical to implement evidence-based reading interventions to optimize student outcomes (Kretlow and Bartholomew 2010). Promising empirical evidence suggests that with effective supports in place, struggling readers with ID and ASD can improve their reading abilities (Hua et al. 2013, Hughes and Fredrick 2006, Woods-Fields et al. 2015).

Federal legislation in the United States requires educators to help all students, including those with disabilities, achieve high academic standards (ESSA 2015, IDEA 2004). Every opportunity should be made available to students to acquire reading skills that may impact academic (e.g. reading, mathematics) and functional (e.g. daily living, self-help) reading (Cannella-Malone et al. 2019). Literacy instruction has become integral to teaching students with disabilities, and effective reading instruction during grade school cannot be taken for granted. To meet the literacy needs of students with ID and ASD, it is essential to identify appropriate reading interventions and provide practitioners with the tools and support needed to implement them in the classroom context (Cannella-Malone et al. 2019).

Reading instruction: academic and functional

In recent years, legislative demands have brought more attention to reading readiness while providing increased exposure to literacy instruction for all students (Woods-Fields et al. 2015). Empirical evidence suggests strategy instruction leads to improved reading outcomes in students with disabilities, including those with ID and ASD (Browder et al. 2006, Cohen et al. 2008, Hua et al. 2013). In special education, reading instruction goals generally fall into one or both of the following categories: to help students learn to read for academic purposes and/or to acquire functional reading abilities. Reading instruction is critical, as both academic and functional reading abilities foster greater levels of independent functioning in individuals with disabilities (Coleman et al. 2012).

Academic reading instruction is implemented when the literacy focus is geared towards the general education curriculum. For example, high-frequency sight word recognition and decoding skills are elements of typical reading instruction for all students, and thus would be classified as ‘academic’ (Cohen et al. 2008). In contrast, ‘functional’ reading is defined as recognition of text and word symbols in the daily environment (e.g. print describing communicative and safety information; Coleman et al. 2012, Dogoe et al. 2011). Though academic and functional reading are defined differently, as are the context in which they are applied, the skill of reading itself is the same.

Both academic and functional reading curricula require systematic instruction (Rohena et al. 2002). A review of the literature by Hill (2016) reported an increase in research evaluating the effectiveness of reading instruction for students with ID. While Hill (2016) found reading investigations to include participants with ID, few interventions were implemented by teachers. Recommendations included increasing the number of experimental investigations measuring the effects of reading interventions on skill acquisition in students with ID. Further, in addition to focusing on the outcome effects alone, Hill (2016) emphasizes the importance of considering the feasibility of the reading interventions. To that end, the author suggests focusing on easy-to-implement interventions that are efficient and appropriate for the classroom setting.

Students with more complex disabilities are often capable of reading when provided with appropriate instruction (Hill 2016). When selecting an intervention, it is essential to consider 1) effectiveness, as measured by skill acquisition, 2) efficiency, as measured by the number of sessions required for students to reach mastery, and 3) practices that will likely increase student independence (Wolery and Gast 1990). Response prompting procedures (e.g. constant time delay [CTD], progressive time delay [PTD], simultaneous prompting [SP]) have been shown empirically to increase acquisition of new skills in students with ID and ASD (e.g. Ault et al. 1988, Horn et al. 2020b; Swain et al. 2015). SP has been shown to be effective and efficient; however, CTD and PTD offer students more opportunities to respond to discriminative stimuli independently (e.g. 4 s; Aldosiry 2020). In review of the literature on CTD and PTD, Walker (2008) found CTD to be more prevalent in research investigations whereby study participants had lower cognitive functioning (e.g. ASD and ID). Further, Walker (2008) suggested practitioners may feel more comfortable implementing CTD over PTD, as the delay interval is fixed rather than progressive. For these reasons, we examined published literature measuring the effects of CTD on reading acquisition in students with ID and/or ASD.

Constant time delay

CTD is a near-errorless strategy whereby a controlling prompt is initially provided at a 0-second delay interval before being withheld for a predetermined period of time (e.g. 4 s) following presentation of the discriminative stimulus (e.g. instruction; Schuster et al. 1988). Prompts used are those with a high probability that the student will perform the desired response (e.g. read the target word aloud). Implementation of CTD entails initially using a 0 s delay interval (i.e. controlling prompt immediately following instruction). The student either responds by providing a prompted correct or prompted incorrect response. After the student responds correctly when prompted over several consecutive trials, the controlling prompt is withheld for a predetermined duration (e.g. 4 s) and that time delay interval remains fixed (Schuster et al. 1988). It is during this time that the student has an opportunity to provide independent responses. Independent correct responses are counted toward criterion. If the student provides an incorrect response or if they fail to respond within the allotted time (i.e. no response), the controlling prompt is offered, and the student has an opportunity to respond (see Figure 1). Redhair et al. (2013) describe how CTD is used to teach reading:

Figure 1.

Constant time delay reading flowchart.

In the case of teaching an individual to read words, CTD would be applied by presenting the written word (e.g., this would be the natural stimulus) and then immediately giving the response prompt (e.g., saying the word in the case of expressive identification; pointing to the word or using physical prompts in the case of receptive identification). Subsequent trials would occur in the same manner, except the time between the natural stimulus (e.g., the presentation of the written word) and the response prompt would be at a preset interval, such as 5 seconds. The interval allows the individual to respond to the stimulus. If no response exists within that preset interval, the trial ends with the response prompt.

Teacher-delivered CTD requires a trained interventionist (e.g. teacher) to implement the time delay procedure with fidelity (Dogoe et al. 2011, Hua et al. 2013). The following example illustrates a practical example of teacher-delivered CTD reading instruction:

Ms. Roberts holds up an index card (on which the word ‘stop’ is written) and says, ‘Read the word,’ and with no hesitation (i.e., 0 s delay interval), she provides a controlling prompt by verbally saying ‘stop.’ Correspondingly, Gavin verbalizes the word ‘stop’ and is praised for offering the correct response. Following two consecutive opportunities with Gavin reading the functional sight word correctly using a 0 s delay interval, Ms. Roberts withholds the controlling prompt for 5 s. If Gavin fails to read the word within the 5s delay interval, Ms. Roberts provides the controlling prompt (i.e., she verbalizes ‘stop’). If Gavin says an incorrect word (e.g., bathroom), Ms. Roberts immediately provides the controlling prompt. This protocol continues until Gavin correctly reads the target functional sight words independently for three consecutive trials, he has reached criterion.

There are also technology-based methods for implementing CTD as a reading intervention (Coleman et al. 2012, Mechling et al. 2007, Yaw et al. 2011). Though procedurally very similar to teacher-delivered CTD, technology-delivered CTD enables students to engage in individualized reading instruction without requiring one-on-one instruction; thus it may be more feasible in the classroom. When implementing CTD, it is essential for the interventionist or computer to present the anticipated response consistently based on a predetermined fixed interval (Pruitt and Cooper 2008). Controlling prompts are faded as the student responds with accuracy to the discriminative stimulus. When using CTD to teach reading, each session typically consists of multiple opportunities for the student to respond (e.g. a list of target sight words).

As described in Figure 1, unprompted correct responses are counted towards criterion mastery (e.g. 90% of words read correctly). An example of an unprompted correct response would be if the student correctly articulates the target word independently when presented with the task direction (e.g. ‘Read the word’). Swain and colleagues (2015) provide a detailed description of other responses, including a) a prompted correct response, b) an unprompted incorrect response, c) a prompted incorrect response, and d) no response (Swain et al. 2015). Accordingly, a prompted correct response is observed when the student correctly articulates the target word within the delay interval (e.g. 4 s), albeit following the instructor’s verbal prompt (model). An unprompted incorrect response is observed when the student articulates a word or phrase other than the target word in response to the task direction. Similarly, a prompted incorrect response is observed when the student articulates a word or phrase other than the target word following the instructor’s verbal prompt. Finally, no response is observed when the student fails to provide a verbal response within the predetermined delay interval following the task direction. Controlling prompts are used, as needed, to promote correct student responding, and the predictable nature of the fixed time delay interval (e.g. 4 s) encourages transfer of stimulus control with few errors (Browder et al. 2009, Horn et al. 2020a). This near-errorless time delay procedure continues until the student reaches a predetermined level of mastery, as measured by percentage of unprompted correct responses (e.g. 100% of words correctly decoded; Cohen et al. 2008). As mentioned above, CTD can be utilized as a technology-delivered reading intervention:

Ms. Roberts, a special education teacher, used technology-delivered CTD to support reading instruction in her class. Presented on the computer screen was the target functional sight word (e.g., bathroom) and four realistic pictures, one in each corner of the computer screen. As the first target word appeared on the screen, a recording made by Ms. Roberts instructed DeAndre to ‘match to picture.’ Initially, the controlling prompt (i.e., correct computer demonstration) is offered at a 0 s delay interval. Once the controlling prompt is withheld for 5 s, DeAndre independently selects the correct picture. Consequently, the target word is automatically read aloud and a praise statement immediately follows. If an incorrect picture is selected or DeAndre does not respond within the delay interval, the computer immediately shows the correct response and reads the word aloud. Mastery is demonstrated as DeAndre provides unprompted correct responses for three consecutive sessions.

Given the paucity of literature specific to teaching reading to students with ID and ASD, coupled with positive learner outcomes resulting from CTD instruction (e.g. skill acquisition that is generalized and sustained over time), we sought to examine empirical research specific to CTD reading interventions for students with ID and ASD. It is well documented that CTD leads to skill acquisition in students with ID and ASD, yet less is known about the effects of applying this evidence-based strategy when teaching reading to the same population of students. Therefore, our purpose for conducting this review of the literature was twofold. The first purpose was to analyze published research measuring the effects of CTD to teach reading for academic and functional purposes. Specifically, we evaluated reading skill acquisition (i.e. effectiveness) as well as trials-to-criterion (i.e. efficacy) across studies. The second purpose was to review the effects across modes of implementation, i.e. with traditional (e.g. teacher-delivered) materials or technology (e.g. computer-assisted).

Method

Search procedures

We conducted a review of the literature to examine the effects of CTD on reading acquisition in students with ID and/or ASD. Relevant peer-reviewed empirical studies covering a 15-year time span (2005–2020) were included in the search. This timeframe was selected to capture published literature on the most recent and relevant ways in which CTD is implemented as a reading intervention when teaching the target population of students. Preliminary search procedures utilized the Educational Resources Information Center (ERIC) and EBSCOhost databases through a web-based university library website. Keywords in the search included full and truncated versions of time delay, constant time delay, constant prompt delay, reading instruction, disabilities, intellectual disability, autism spectrum disorder, academic reading, functional reading, and mental retardation. Authors conducted a secondary search, which consisted of examining reference lists and retrieving qualifying published articles accessible through the university library database or Google Scholar.

The initial search resulted in the retrieval of 33 articles. After reviewing titles, keywords and abstracts, 17 relevant articles were identified independently by the first two authors. The subsequent step involved conducting a full-text analysis. Articles were included based on the following inclusion criteria: (a) the study measured the effects of CTD (i.e. acquisition) on reading; (b) instruction targeted academic or functional reading skills; and (c) participants consisted of school-aged children or young adults with a primary diagnosis of ID or ASD. Nine studies met criteria, were independently agreed upon and selected by the authors, and were included in the review. Although our search was inclusive of all levels of ID, no studies that measured the effects of CTD on reading acquisition in students with severe disabilities were located. Therefore, this review includes research on students with ID in the mild or moderate ranges only, and ASD.

Data analysis

As depicted in Table 1, studies were analyzed according to methodological details pertaining to the a) participants, b) design, c) purpose, d) reading content (i.e. functional or academic), e) CTD delivery (i.e. teacher-delivered or technology-based instruction), f) CTD features (e.g. time delay interval applied), and g) results. Study findings and visual analyses were examined.

Table 1.

Content across studies

Article	Participants	Design	Purpose	Reading content	CTD delivery	CTD features	Results
Akcin (2013)	3 students with ASD, ages 12–14	Adapted alternating treatments research design	Compare effectiveness of CTD and stimulus fading strategies when teaching sight words	Academic (sight words)	Traditional		Target words were acquired, generalized, and maintained; thus, both strategies were effective. CTD was more efficient
Aldosiry (2020)	4 students with mild-moderate ID, ages 7–9	Adapted alternating treatments research design	Compare efficacy of CTD and SP on decoding and reading new words	Academic, no technology Flashcards	Traditional, teacher-led instruction	5 s delay interval	CTD and SP resulted in improved decoding skills. CTD was more efficient, as measured by trials to criterion; however, SP resulted in fewer error rates and reduced instructional time
Cohen et al. (2008)	5 students with mild-moderate ID, ages 9–14	Multiple-probe research design	1) Measure the effects of CTD with a 3-step decoding strategy 2) Measures included decoding efficiency of new words or relevant phonemic structures and generalization of the decoding strategy	Academic, no technology	Traditional, teacher-led instruction	4 s delay interval	Participants learned to decode and read target words with the 3-step decoding strategy and CTD. All participants improved efficiency in learning new words
Coleman et al. (2012)	2 students with moderate ID; 1 student with ASD, ages 10–12	Alternating treatments research design	Compare effectiveness and efficiency of 2 CTD interventions: Teacher-directed vs. Computer-assisted (PowerPoint)	Functional (sight words) Computer-assisted (i.e. PowerPoint) vs. no technology	Traditional, teacher-led and technology-based instruction	4 s delay interval	Percentage of words ready correctly increased as a result of CTD instruction. Students with ID required fewer trials-to-criterion with teacher-directed CTD Computer-assisted CTD was more efficient for students with ASD
Dogoe et al. (2011)	2 young adults with ASD, ages 23–24	ABC research design	1) Measure the effects of CTD on reading key words found on product warning labels & acquire contextual meaning of keywords 2) Generalizability to actual products (e.g. cleaning supplies)	Functional, no technology Flashcards	Traditional, teacher-led instruction	5 s delay interval	Both adults with ASD learned to read, define and give contextual meanings of target key words on product warning levels Participants required 136 trials for reading, 141 for definition, and 156 for contextual meaning
Hua et al. (2013)	4 students with ID, ages 19–21	Alternating treatments research design	1) Evaluate effectiveness of CTD on vocabulary acquisition and retention 2) Measure participants’ ability to comprehend expository text following vocabulary instruction	Academic, no technology Flashcards	Traditional, teacher-led instruction	3 s delay interval	Using CTD when teaching vocabulary increased acquisition and retention of target words Participants maintained increased vocabulary retention post-intervention No notable change in comprehension of expository texts
Mechling et al. (2007)	3 students with moderate ID, ages 19–20	Multiple-probe research design	Measure effectiveness of interactive computer-assisted instruction (CAI) coupled with CTD during small group instruction on reading grocery words and match pictures of grocery items to corresponding target words and items	Functional CAI: PowerPoint on SMART board	Technology-based instruction	3 s delay interval	Participants learned to read target grocery words and match target grocery words to corresponding photo and item High levels of sustainability across participants
Swain et al. (2015)	3 students with moderate ID, and 1 student with ID and ASD, ages 8–11	Adapted alternating treatments research design	Compare efficacy of CTD and SP on functional sight word acquisition	Functional (sight word) Flashcards	Traditional, teacher-led instruction	5 s delay interval	Participants acquired reading skills. SP required less instructional time, whereas CTD resulted lower error rates. Efficiency data were mixed
Yaw et al. (2011)	1 student with ASD, age 12	Multiple baseline research design	1) Evaluate effectiveness of computer-based sight-word reading system (CBSWRS) paired with CTD procedures during sight-word instruction	Academic CBSWRS through PowerPoint	Technology-based instruction	2 s delay interval	CBSWRI and CTD together resulted in increased sight-word reading for participant Acquired sight-words were generalized and maintained post-treatment

Note. CTD = constant time delay; SP = simultaneous prompting.

Results

All studies evaluated the effects of CTD, as measured by reading skill acquisition, in students with ID and/or ASD. A few investigations included in our review reported efficiency (i.e. trials-to-criterion, error rates), generalization, and/or maintenance measures. Participant ages and disability diagnoses are shown on Table 1. Educational placements primarily consisted of restrictive (i.e. adapted curriculum) classroom settings. Experimental control was achieved in each study using a single-case research methodology. The specific design for each investigation is indicated in Table 1. Studies were analyzed for intervention elements that aligned with the stated aims of this review.

Reading content

All nine studies measured the effects of CTD on either academic or functional reading achievement. Results suggest that when students are systematically prompted using CTD, noticeable gains in reading ability are observed (Akcin 2013, Aldosiry 2020, Cohen et al. 2008, Coleman et al. 2012, Dogoe et al. 2011, Hua et al. 2013, Mechling et al. 2007, Swain et al. 2015, Yaw et al. 2011).

Academic reading instruction

Five studies in this review identified CTD as an effective intervention when used to teach academic reading skills (i.e. the acquisition of high-frequency sight-words, decoding skills, and vocabulary comprehension) to students with ID or ASD (Akcin 2013, Aldosiry 2020, Cohen et al. 2008, Hua et al. 2013, Yaw et al. 2011). Although the aforementioned studies measured the effects of CTD on the acquisition of specific academic reading content, there were differences in the aims and scope across reviewed research. Simply, there were differences in the types of reading skills measured across studies. For example, Yaw et al. (2011) implemented the CTD procedure during sight-word reading instruction. Findings showed that using a 2 s delay interval coupled with a technology-based sight-word reading system resulted in acquisition and generalization of target sight words in a student with ASD. In contrast, Cohen et al. (2008) combined CTD with a multi-step decoding strategy, and all participants (n = 5) learned to decode and read target words as a result. Further, efficiency data showed participants increased the rate in which they acquired new words. Similarly, Hua et al. (2013) found CTD to result in acquisition of unknown vocabulary embedded in expository texts across young adult participants. That is, that 84% of the unfamiliar words were acquired across study participants (n = 4) and 50% of those words were retained after the CTD intervention was removed. Two comparative studies measured the effects of CTD and an independent strategy (e.g. stimulus fading, simultaneous prompting) on academic reading skill acquisition (Akcin 2013, Aldosiry 2020). Akcin (2013) measured the effects of CTD on sight word acquisition, whereas Aldosiry (2020) focused on decoding skills. Both investigations led to increased reading abilities across all participants, and CTD was shown to be a more efficient instructional approach across comparative research. In other words, participants required fewer trials-to-criterion with CTD compared to stimulus fading (Akcin 2013) and simultaneous prompting (Aldosiry 2020). However, Aldosiry (2020) found simultaneous prompting to result in fewer student errors and less instructional time when compared to CTD.

Functional reading instruction

The effects of CTD on teaching functional reading skills were measured in four investigations (Coleman et al. 2012, Dogoe et al. 2011, Mechling et al. 2007, Swain et al. 2015). Target reading skills included reading common recipe vocabulary words (Coleman et al. 2012), product warning labels (Dogoe et al. 2011), grocery words (Mechling et al. 2007), and food/restaurant words (Swain et al. 2015). Participants across all four studies (n = 12) learned to read target words as a result of the CTD intervention. Dogoe et al. (2011) evaluated the effects of CTD on teaching two young adults with ASD to read, define, and identify the contextual meaning of target words on a product warning label. Both participants acquired target reading skills with few errors reported. Both Coleman et al. (2012) and Dogoe et al. (2011) included generalization measures affirming participants’ abilities to apply newly acquired functional reading skills in the natural environment. Mechling et al. (2007) did not include generalization measures, but intervention data collection revealed that CTD instruction was successful in teaching participants with ID to read target grocery words, match grocery items and photos to corresponding words, and read other students’ grocery words through observational learning.

In a comparative investigation, Swain et al. (2015) found benefits to both CTD and simultaneous prompting (SP). When teaching students with moderate ID and students with moderate ID and ASD to read functional sight words, CTD resulted in fewer errors. However, SP required less instructional time. Efficiency data (i.e. the number of sessions needed to reach criterion) revealed CTD to be more efficient for two of the four participants, whereas SP was more efficient for the other two participants (Swain et al. 2015). Further, both CTD and SP were found to be equally effective in generalizability to classroom and community contexts, and follow-up data revealed participants sustained acquired functional reading skills over time, regardless of the instructional method (Swain et al. 2015). In sum, reviewed research supports CTD as an effective intervention for teaching functional reading skills to students with ID and ASD (Coleman et al. 2012, Dogoe et al. 2011, Mechling et al. 2007). Additionally, comparative research showed SP to also be an effective reading intervention (Swain et al. 2015).

Constant time delay delivery

Studies in this review used both teacher-delivered and technology-based modes for delivering the CTD intervention. Teacher-delivered CTD (e.g. flashcards) was measured in six studies (Akcin 2013, Aldosiry 2020, Cohen et al. 2008, Dogoe et al. 2011, Hua et al. 2013, Swain et al. 2015). Technology-based CTD was implemented in two studies (Mechling et al. 2007, Yaw et al. 2011). Coleman and colleagues (2012) compared the efficacy of the two CTD delivery modes, teacher-delivered and technology-based. Findings specific to CTD delivery modes will follow.

Teacher-delivered constant time delay

Teacher-delivered CTD reading interventions were more prevalent in the research compared to technology-based interventions, and these studies included participants with ID (n = 18) as well as participants with ASD (n = 7). There was some variance in measures across teacher-delivered CTD studies. As shown on Table 1, teacher-delivered interventions accounted for two investigations measuring functional reading (Dogoe et al. 2011, Swain et al. 2015), whereas four studies measured the effects of teacher-delivered CTD on the acquisition of academic reading skills (Akcin 2013, Aldosiry 2020, Cohen et al. 2008, Hua et al. 2013). Despite noted variations in the aims and focus across teacher-delivered CTD reading research, all study participants acquired target skills, and investigations that included follow-up data (e.g. Akcin 2013, Hua et al. 2013) showed once participants reached criterion, newly learned reading skills (academic and functional) were sustained over time (i.e. 1 day − 3 weeks post-treatment).

Technology-based constant time delay

Researchers in two investigations integrated technology to measure the effects of CTD on reading acquisition (Mechling et al. 2007, Yaw et al. 2011). Participants in technology-based CTD reading research included students with ID in the moderate range (Mechling et al. 2007) as well as one participant with ASD (Yaw et al. 2011). Technology-based CTD research measured the effects of the independent variable on acquisition of both academic (Yaw et al. 2011) and functional (Mechling et al. 2007) reading skills. Mechling et al. (2007) conducted the intervention during small group instruction. Specifically, a SMART board™ displayed the PowerPoint-delivered CTD reading intervention and participants engaged in instruction together, which consequently facilitated observational learning in addition to targeted functional reading acquisition (Mechling et al. 2007). In contrast, Yaw et al. (2011) measured the effects of a technology-delivered CTD reading intervention with one student using a computer-based sight word reading system to teach academic reading skills. Despite the methodological differences between the two technology-based CTD reading investigations, both interventions were effective, as evidenced by positive reading outcomes across participants.

Coleman et al. (2012) conducted a comparative investigation, examining the effects of technology-based (i.e. PowerPoint) and teacher-delivered CTD while teaching functional sight words to two students with ID in the moderate range and one student with ASD. Both CTD procedures were found to be effective interventions, as measured by increased acquisition of functional sight words in study participants. The heterogenous nature of the participants yielded efficiency and preference differences between the two participants with ID and one student with ASD. Participants with ID required fewer trials-to-criterion and also displayed a preference for teacher-delivered CTD instruction compared to technology-based CTD. In contrast, the technology-based CTD method was more efficient, as measured by trials-to-criterion, for the participant with ASD, who also displayed a preference for that instructional modality (Coleman et al. 2012). These conclusions are consistent with findings from Yaw et al. (2011), demonstrating increased reading outcomes in a student with ASD when CTD was implemented along with a technology-based sight word reading system.

Discussion

In conducting this review of the literature, we analyzed published empirical investigations measuring the effects of CTD as a reading intervention used to teach students with ID and/or ASD. The results of our review suggest school-aged children and young adults with ID and ASD can improve academic and functional reading abilities when receiving CTD instruction (Cohen et al. 2008, Coleman et al. 2012, Dogoe et al. 2011, Hua et al. 2013, Mechling et al. 2007, Yaw et al. 2011). Our findings extend the research base on CTD by adding the focus on reading skill acquisition in a unique population of learners. We recommend considering CTD when teaching both academic and functional reading skills to students with ID and ASD.

In comparing teacher-delivered and technology-based modes of implementation of CTD results are mixed at best. According to teacher reports, computer-based CTD instruction is less demanding on teachers, which suggests technology-based CTD reading instruction may be more feasible for practical application in comparison to the teacher-delivered method (Yaw et al. 2011). However, such decision-making should be individualized to ensure students’ needs are properly met, as student preference and resource availability and effectiveness regarding modes of implementation varied based on the findings of this review. Mechling et al. (2007) found students with ID who preferred teacher-delivered CTD had more success with that mode of implementation during intervention, as measured by trials-to-criterion. The participant with ASD who showed a preference for technology-based CTD had more success with that mode of implementation (Mechling et al. 2007).

Teacher-delivered CTD reading interventions have utilized flashcards (e.g. Dogoe et al. 2011), whereas technology-based CTD reading interventions have employed interval-controlled PowerPoint presentations (e.g. Coleman et al. 2012, Yaw et al. 2011). Researchers suggest using technology to aid reading instruction allows for individualized learning while reducing teacher demands (Yaw et al. 2011). It should be emphasized that resources (both personnel as well as technology) may be critical to determining which technology is implemented. Meaning, there must be a goodness of fit between available technology, the teachers’ ability to program CTD procedures (i.e. presentation of target words with controlling prompt), and students’ ability to independently use and respond to computer software.

CTD is an evidence-based practice that requires attention to task and memory skills. The effectiveness of CTD for students with cognitive challenges lies in its individualization. That is, the time delay following a prompt (e.g. 2 s, 5 s) is adjusted to meet the needs of the student, therefore findings from the reviewed studies are determined by the ability of the participants. Study participants across the reviewed research (n = 28) showed gains in target reading skills as a result of a CTD intervention

Limitations

Results from this review of the literature should be interpreted within the context of several limitations. The first limitation relates to generalization of our findings. We deemed nine studies appropriate for inclusion, which rendered a small population of students (n = 28), all of whom had a diagnosis of ID and/or ASD; thus, students with other disability diagnoses (e.g. learning disabilities, emotional disturbance) may respond differently to the reading intervention. Additionally, reviewed research examined the effects of CTD on reading instruction only. Therefore, findings are limited and should be interpreted within that context. The second limitation relates to search procedures. Initial search procedures consisted of utilizing two widely used educational data bases (i.e. ERIC and EBSCOhost), and secondary search procedures followed. However, limiting our initial search to specific databases could have inadvertently resulted in the exclusion of relevant research. Finally, the third limitation involves the scope of the content and time span of this review. That is, reviewed research was specific to CTD and did not include published articles on other evidence-based reading interventions. Further, the research reviewed was limited to a 15-year time span to ensure the newest technology and techniques being employed, yet it is possible earlier findings could have brought about different outcomes. Despite these reservations, the present review extends the literature on CTD by focusing on reading acquisition in students with ID and ASD. Additionally, our review underlines the need for future research in this area.

Implications for research and practice

After examining published research measuring the effects of CTD on reading acquisition in students with ID and ASD, several implications for research and practice present themselves. Given the extensive research base supporting the use of CTD when teaching students with ID and ASD, researchers should extend the line of research on CTD as a reading intervention. With recent interruptions to in-person schooling caused by the global COVID-19 pandemic, researchers have an opportune moment in time to focus specifically on technology-based CTD reading interventions.

Overall, this review supports the practical application of CTD as a reading intervention when teaching students with ID and ASD. For that reason, we recommend special education teachers consider the use of CTD to teach both academic and functional reading objectives to these students. As teacher-delivered and technology-based CTD methods were shown to result in increased reading skills in participants, special education teachers would benefit from utilizing these methods during reading instruction when working with students with ID and ASD.

Teacher-directed CTD reading instruction is a low-cost approach commonly implemented with flashcards. To ensure CTD is implemented with fidelity, the teacher interventionist must be trained, and sessions require one-on-one or small-group instruction. However, teacher-made flashcards can be used to teach reading to multiple students who have similar goals (Akcin 2013).

Other CTD reading methods utilize technology (e.g. PowerPoint presentation on a computer; Yaw et al. 2011). Though may not be as cost-effective as flashcards, integrating technology when implementing CTD to teach reading has been shown to be effective and reduces demands on the special education teacher (Coleman et al. 2012). Much of the equipment used to support technology-based CTD is relatively low-tech (e.g. computer), and may be readily available to special education teachers. Given the abrupt interruptions to special education services followed by transitioning to virtual learning for students with disabilities in light of the COVID-19 pandemic, the need for effective learning methods to improve reading abilities in students with ID and ASD has become more important than ever. It is plausible to think technology-based CTD reading instruction is an evidence-based practice would be appropriate to implement in both classrooms and virtual learning environments.

Conclusion

CTD is an evidence-based practice with more than 30 years of empirical support. However, much of the published CTD research has not been specific to reading skill acquisition. This review of the literature examined published studies that measured the effects of CTD on reading attainment (academic and functional) in participants with ID and/or ASD. Research findings suggest that CTD may be an efficacious reading intervention when used to teach students with ID and ASD. Additionally, and perhaps most importantly, CTD is an economically-friendly intervention that can be implemented by a teacher (i.e. teacher-delivered CTD), or technology can be utilized for instruction (i.e. technology-based CTD). Both methods led to positive learning outcomes, and technology-based CTD is less demanding on the teacher and holds promise in its applicability in other learning environments (e.g. virtual learning). Replication of the reviewed research and utilization of CTD interventions observed over time will determine the success and ultimate utility of the results of these studies and this literature review.

Conflict of interest

No potential conflict of interest was reported by the authors.