Objective: Psychoeducation forms part of the current practice for ADHD; however, its efficacy is yet to be established. Method: Sixty-nine children/adolescents with ADHD were randomly assigned for their families to receive either a well-structured psychoeducation program (n = 35), or belong to a control group (treatment-as-usual, n = 34). Results: One-way analyses of variance showed a statistically significant Treatment x Time interaction, for ADHD total symptoms, inattention/cognition, and hyperactivity/impulsivity subdomains according to the parents, the first two with medium-large effect sizes. The effects of the intervention on the ADHD total and the inattention/cognition domain persisted after 6 months follow-up. No significant differences in teacher ratings were found; however, an improvement in clinical functioning as measured by clinicians was observed. Conclusion: This psychoeducation program has shown effectiveness in reducing ADHD symptoms when compared with treatment as usual. Psychoeducation needs to be considered as a valid and additional approach in ADHD.