Table 1.

Data extraction: Quantitative studies.

Author	Title	Language	Outlet (journal name/other outlet/dissertation/unclear)	Year	Study location	Type of school and educational setting	Type of special need	Child age (mean and range)
Metzner (1926)	Size of class for mentally retarded children	English	The Training School Bulletin	1926	Detroit, U.S.	Type of school not specified, but setting is probably half‐time.	Mental retardation	Approximately an average of 10.8, range not reported.
Forness (1985)	Effects of class size on attention, communication, and disruption of mildly mentally retarded children	English	American Educational Research Journal	1985	California, U.S.	Not specified, but it is probable that all students spent more than half their day in special class, and that regular class integration was limited to non‐academic classroom periods during the afternoons.	Mildly mentally retarded (educable)	Mean age in small classes 12.3; medium classes 11.0; large classes 11.2; overall 11.3.
MAGI Educational Services, Inc. (1995)	Results of a Statewide Research Study on the Effects of Class Size in Special Education	English	Class Size Research Bulletin	1995	New York, U.S.	Modified Instructional Services (MIS) I classes which covered classes for students who required instructional services in a special class with opportunities for mainstreaming. Students could supposedly spend both full‐time or less in these classes, depending on pull‐out services or involvement with mainstream classrooms.	The majority of MIS I students were classified as learning disabled.	Not reported, but both elementary and secondary students.

Author	Child ethnic, cultural, and language background	Child SES	Child gender	Teacher education and experience	Study design	Class size	Intensity (size of reduction)	Duration of class size reduction
Metzner (1926)	Not specified	Not specified	Varies between 47.5% and 71.1% boys in treatment groups; in control group 64% boys.	Not specified		Treated are three classes with 15 students, three classes with 20 students, three classes with 25 students, and three classes with 30 students; controls are 12 classes with 22 students.	A reduction of 2 and 7 and an increase of 3 and 8.	180 days
Forness (1985)	Not specified	Not specified	Small classes: 50% male; medium classes 58% male; large classes 56% male; overall 56% male.	Not specified		5 small classes (10–13), 14 medium classes (14–16), and 7 large classes (18–21).	Mean difference between small and medium classes is 2.5 students, and between medium and large classes 4 students.	Not specified, but presumably most subjects had been in EMR (special education) classes for at least several months.
MAGI Educational Services, Inc. (1995)	Not specified	Not specified	Not specified	Not specified	Quasi‐experimental observation study	Students and teachers were randomly selected from two class size options: 12:1 and 15:1. Actual number of students observed in the classrooms was generally much lower than the number of students registered.	Formally an increase in some classrooms from 12:1 to 15:1 (so an increase of 3).	Not specified

Author	Type of data (Independent observation/Questionnaire/Other)	Format (Continuous/Categorical/Dichotomous)	Number of measures and timing	Type(s) and name(s) of outcomes (Academic Achievement/Socioemotional outcomes/Wellbeing/Student classroom behaviour (please state name of outcome, e.g. SDQ))	Sample size	Means/regression coefficients/t‐ and F‐statistics/Other	Standard deviations
Metzner (1926)	Pressy first grade reading test was given to those who had done no academic work beyond first grade, and the Stanford Achievement Test for grade 2 and 3 was given to the remaining.	Continuous	Experiment lasted 180 days, tests taken before and at the end.	Reading. Pressy Reading Test and Stanford Achievement Test.	Treated are three classes with 15 students, three classes with 20 students, three classes with 25 students, and three classes with 30 students (total: 270); controls are 12 classes with 22 students (total: 264).	Pre‐test scores and gain scores, Tables 1 and 2.	No SD's reported.
Forness (1985)	The outcome (behaviour) was recorded on each child in specific categories of classroom functioning using an observation system described in detail in Forness, 1983 (available on request from the senior author, i.e. not published).	Percentage of time with a specific behaviour.	Data gathered in April, year not reported.	Behaviour divided into four pre‐determined categories: (a) communication‐ task‐oriented verbal or gestural response (e.g., pupil asks or answers a question, recites or raises hand); (b) attend‐ eye contact to teacher, task materials, or peer who is reciting; (c) not attend‐ eye contact not directed to teacher, task materials, or pupil who is reciting; and (d) disrupt‐behaviour incompatible with on‐task activities (e.g., talks to another pupil when not permitted, speaks out of turn, hits classmates, or throws objects).	26 classes and 393 students. 5 small classes (10–13) with 61 students, 14 medium classes (14–16) with 202 students, and 7 large classes (18–21) with 130 students.	Outcome reported as percentages. The total for each behaviour was computed across all response conditions for each subject. The percentage of time each child received a response from teachers was computed across all types of behaviour as a measure of time the teacher appeared to be involved with each subject, and the same was computed for classmate as a measure of the relative amount of time each subject appeared to interact with peers. Mean percentage by group is reported and overall mean and SD. Table 4.	Table 4
MAGI Educational Services, Inc. (1995)	Two standardised observational instruments were used.	Percentage of time with a specific behaviour.	Not specified	Classroom behaviour observed with: The Code for Instructional Structure and Student Academic Response (MS‐CISSAR), and The Instructional Environment System (TIES II).	753 elementary and secondary students and 203 teachers were randomly selected from the two class size options (12:1 and 15:1).	Percentage of time engaged in different classroom behaviours.	Not reported