A Cochrane review included 25 studies. The results suggest that speech and language therapy is effective for children with phonological (SMD=0.44, 95%CI: 0.01 - 0.86; 7 studies, n=264) or vocabulary difficulties (SMD=0.89, 95%CI: 0.21 - 1.56; n=136), but that there is less evidence that interventions are effective for children with receptive difficulties (SMD=-0.04, 95%CI: -0.64 - 0.56; 2 studies, n=193). Mixed findings were found concerning the effectiveness of expressive syntax interventions (SMD=1.02, 95%CI: 0.04 - 2.01; n=233). No significant differences were shown between clinician administered intervention and intervention implemented by trained parents, and studies did not show a difference between the effects of group and individual interventions (SMD=0.01, 95%CI: -0.26 - 1.17; one study, n=216). The use of normal language peers in therapy was shown to have a positive effect on therapy outcome (SMD=2.29, 95%CI: 1.11 - 3.48; one study, n=20).
Comment: The quality of evidence is downgraded by study quality (unclear allocation concealment) and inconsistency (heterogeneity in treatments).