In 2005 we established the first American-style summer treatment program (STP) for children with attention deficit hyperactivity disorder (ADHD) located outside North America. This program was based on methods established by professor Pelham and has been used in a number of studies and at a number of sites in the USA. A total of 137 children diagnosed with ADHD, ranging in age from 6 to 12 years, participated in at least one of five annual summer treatment programs in Kurume city, Japan, during 2005-2009. The duration of the STP was 2 weeks in 2005, 2008, and 2009; 3 weeks in 2006 and 2007. A set of evidence-based behavioral modification techniques comprising the STP behavioral program (e.g., point system, daily report card, positive reinforcement, time out) was used. We also assessed the cognitive function of individual children before and after STP using the CogState(R) batteries. Every year, regardless of the duration of the STP, most children showed positive behavioral changes in multiple domains of functioning, demonstrated by significant improvement in points earned daily, which reflect behavior frequencies. Cognitive functions, particularly the rate of anticipatory errors in executive function, significantly improved after the STP, suggesting that STP has positive effects not only on behavioral aspects but also on some cognitive functions. Further studies are necessary to confirm this finding by studying sequential cognitive function of age-matched children who do not attend STP.