This was an individual participant data meta-analysis. It pooled 25 randomized controlled trials of behavioral treatments, such as parent training, classroom programs and skills training, for children and teenagers with ADHD under 18. It covered 2,885 young people (1,936 who received treatment and 949 controls), with a mean age of about 9 years (8.78) and ages from 2 to 17.5. The trials came from the USA, the Netherlands, the UK, Germany, Iran, Israel and New Zealand.
When rated by the person closest to the treatment, usually a parent, behavioral treatment lowered ADHD symptoms and daily impairment. The effects were small to medium (total ADHD symptoms b = -0.42; global impairment b = -0.59, where negative means improvement). But when outcomes were rated by observers who probably did not know who got treatment, no effect was found. Those blinded ratings came only from a few preschool studies.
Children with more conduct problems or a conduct disorder, higher ADHD severity, or a single parent showed larger gaps from controls. The authors say this was because untreated children got worse, not because treated children improved more, so they read it as treatment guarding against decline. They suggest these groups be prioritized for behavioral treatment.
Source: Annabeth P. Groenman, Rianne Hornstra, Pieter J. Hoekstra, et al.. An Individual Participant Data Meta-analysis: Behavioral Treatments for Children and Adolescents With Attention-Deficit/Hyperactivity Disorder. Journal of the American Academy of Child & Adolescent Psychiatry (2021). doi:10.1016/j.jaac.2021.02.024