OBJECTIVE. We examined the effect of the Cognitive-Functional (Cog-Fun) occupational therapy intervention on executive functions and participation among children with attention deficit hyperactivity disorder (ADHD). METHOD. We used a randomized, controlled study with a crossover design. One hundred and seven children age 7-10 yr diagnosed with ADHD were allocated to treatment or wait-list control group. The control group received treatment after a 3-mo wait. Outcome measures included the Behavior Rating Inventory of Executive Function (BRIEF) and the Canadian Occupational Performance Measure (COPM). RESULTS. Significant improvements were found on both the BRIEF and COPM after intervention with large treatment effects. Before crossover, significant Time Group interactions were found on the BRIEF. CONCLUSION. This study supports the effectiveness of the Cog-Fun intervention in improving executive functions and participation among children with ADHD.