The objective of this study was to evaluate the effectiveness of an 8-week behavioral and social skill (BSS) class for children newly diagnosed with attention-deficit hyperactivity disorder (ADHD) and their parents, initiating stimulant treatment in primary care. The subjects were 100 children, aged 5 to 12 years, recently diagnosed with ADHD and treated with stimulant medication, and their parents or guardians. Eligible families were randomly assigned to an intervention group (IG: n = 59) or control group (CG: n = 41). The BSS function of each child was assessed using DuPaul's ADHD Parent Rating Scale (18-item) and Child Attention Profile (12-item) during blinded baseline and follow-up interviews. Parent discipline practice was assessed using a five-item inventory based on Likert-scale ratings during identical periods. Computerized pharmacy records were used to track psychostimulant use over time. IG children exhibited significantly lower parent-rated ADHD symptoms, whereas IG parents reported significantly better and more consistent discipline practices compared with CG parents across time. No significant differences were found between groups in Child Attention Profile scores across time. Psychostimulant use did not significantly differ between groups across time. BSS training was well accepted and seemed to significantly improve BSS functioning among IG children in the home setting only.