Summary of findings for the main comparison. Parent‐mediated intervention versus treatment as usual for communication and language development in young children with Down syndrome.

Parent‐mediated intervention versus treatment as usual for communication and language development in young children with Down syndrome
Patient or population: children with Down syndrome aged between birth and six years Setting: home, clinic, or both; interventions delivered through group or one‐to‐one sessions Intervention: parent‐mediated intervention Comparison: treatment as usual
Outcomes	Impact	№ of participants (studies)	Certainty of the evidence (GRADE)
Expressive language (number of (different) target words) Assessed with: parent reports, language sample, experimental task Follow‐up: 3 weeks	1 study found that the intervention did not increase the children's overall vocabulary size on a standardised parent report. However, parents in the study reported that the intervention group used almost 5 more targeted words than the control group (P < 0.05), postintervention. Children who received treatment also used almost 2 more target words in free‐play interaction with their mothers than those in the control (P < 0.05), although no differences were noted in the production of these target words in a semi‐structured experimental task	12 (1 RCT)	⊕⊝⊝⊝ Very lowa,b,c,d
Receptive language (total language; standard scores) Assessed with: direct assessment; parent reports Follow‐up: 2 months	1 study found that children in the intervention group made a 50% increase in their 'language' scores (P < 0.01) using direct assessment, and a 47% increase in their 'language‐cognitive' scores (P < 0.01) using parent reports, compared to just 12% and 3% increases respectively in the control group	15 (1 RCT)	⊕⊝⊝⊝ Very lowa,b,d
Parental stress	Not measured
Changes in parental behaviour/responsivity Assessed with: observational rating scales (not specified); Maternal Behaviour Rating Scale (Likert scale scored 1‐5; higher scores indicate increased use of coded behaviour); self‐reports Follow‐up: range 3 weeks to 2 months	1 study found that mothers in the intervention group used almost 3 more target labels (P < 0.05), almost 7 more focused stimulation of target labels (P < 0.001) and maintained a more stable rate of talk (P < 0.05) compared to those in the control group. However, the mothers did not use more complex language than those in the control group postintervention. Qualitative information found that mothers also reported changes in the way they communicated with their children after the intervention, which was confirmed through checklists completed by clinicians following home visits	27 (2 RCTs)	⊕⊝⊝⊝ Very lowa,d
	1 study found that mothers in the intervention group made a 67% increase (P < 0.001) in their 'responsiveness' ratings and a 56% increase (P < 0.001) in their ratings on 'affect', compared to the control group increases of 13% and 6%, respectively. The intervention group also reduced their ratings on 'achievement/directiveness' by 27% (P < 0.01), compared to a 3% reduction in the control group, postintervention
Socialisation Assessed with: direct assessment; parent reports; Child Behaviour Rating Scale (Likert scale scored 1‐5; higher scores indicate increased use of coded behaviour) Follow‐up: 2 months	1 study found that children in the intervention group increased their social development quotient scores on direct assessment by 50% (P < 0.01) and on parent reports by 44% (P < 0.01), compared to 13% and 3% increases, respectively, in the control group. A rating scale also found that the intervention group increased their ratings in attention by 54% (P < 0.001) and initiation by 57% (P < 0.001), compared to 11% and 7% in the control group, respectively	15 (1 RCT)	⊕⊝⊝⊝ Very lowa,b,d
Language attrition Assessed with: parent reports; direct assessment; language samples; experimental task Follow‐up: range 3 weeks to 2 months	No studies reported evidence of language attrition in the intervention or control group at postintervention	27 (2 RCTs)	⊕⊝⊝⊝ Very lowa,d
Adherence to treatment Assessed with: consumer questionnaire; observation checklists (not specified) Follow‐up: 3 weeks	1 study found that mothers in the intervention group attended at least 7/9 training sessions and all 4 home visits	12 (1 RCT)	⊕⊝⊝⊝ Very lowa,b,c,d
CI: confidence interval; RCT: randomised controlled trial.
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect.

^aDowngraded by two levels as the sample size was not justified and was small, and the analysis involved a narrative synthesis and so estimates are not available.
 ^bDowngraded by one level as it is not possible to measure inconsistency from a single study.
 ^cDowngraded by one level as the control group had a cointervention in one study.
 ^dDowngraded by two levels as the risk of bias was judged to be high or unclear risk for most factors.