Twenty-five RCTs (963 children) were included.
One study was rated as good, 13 as fair and 11 as poor quality; only the results of good- and fair-quality studies are discussed below. Limitations included small sample sizes, lack of consideration of potential confounders, and disparate methods of assessment, intervention and outcome measurements.
Children aged 0 to 2 years.
No studies exclusively assessed this group. One study enrolled children aged 18 to 42 months. This study reported significant improvements for some, but not all outcomes in the intervention compared with the control group following treatment for receptive auditory comprehension.
Children aged 2 to 3 years (1 good-quality and 6 fair-quality studies).
The studies found improvements on a variety of communication-related outcome measures following clinician-directed expressive and receptive language treatment, parent-directed treatment for expressive delay, and clinician-directed receptive auditory comprehension. Three studies reported no differences between treatment groups for clinician-directed expressive or receptive language therapy (2 studies), parent-directed expressive or receptive therapy (1 study), or parent-directed phonology treatment (1 study). Three studies reported increased socialisation skills, improved self-esteem and improved play themes in children in the intervention groups. One study reported decreased parental stress and another reported increased positive feelings from parents towards their children. One study found no differences between the intervention groups in well-being, level of play and attention, and socialisation.
Children aged 3 to 5 years (7 fair-quality studies).
Five studies reported significant improvements in children in the intervention groups compared with controls; 2 studies reported no differences. Both group-based and clinician-directed interventions improved expressive and receptive symptoms.
No studies provided data on adverse effects or other additional effects of the interventions.