Behavioral parent training (BPT) is recognized as an effective part of the care offered to children with attention deficit hyperactivity disorder (ADHD). The aim of this pilot study was to objectively examine the effect that this intervention may have on motor activity, in addition to the measures classically found in this type of study. Parents of 24 school-aged children (6-12 year) with ADHD who met eligibility criteria were enrolled in the study. Before, after and five months after the intervention, we used three-dimensional accelerometers over one-week periods to measure the children's motor activity, and questionnaires for parental stress, quality of life, ADHD symptoms, anxiety and sensory disorders. To measure motor activity, a control group of normotypic children matched for age, sex and socio-professional category was set up. The experimental group showed slight decreases in motor activity compared with the control group, particularly in the classroom. The intervention showed improvements for parents in average stress and quality of life, and for children in average intensity global ADHD symptom, inattention, opposition and aggression, in line with previous studies on the effectiveness of BPT. The trial is the first clinical study to assess the effects of BPT on motor activity in children with ADHD.