Disruptive behavior problems are among the most prevalent mental health conditions for young children, and they carry significant risks for later socioemotional, conduct, and academic problems, such as substance abuse, delinquency, and school failure. How parents handle these challenging behaviors strongly influences their children's long-term trajectory. Evidence-based parenting programs have shown much value in reducing early-onset disruptive behavior problems, thereby reducing risks for later substance abuse and other behavioral health problems. The reach of parenting programs is limited, however, by significant challenges in recruiting, engaging, and retaining parents, such that most parents who could benefit from parenting assistance never receive it. A public health approach for improving parenting practices that makes evidence-based parenting programs widely available and accessible in a range of formats could reduce the prevalence of disruptive behavior problems, and thus the population-level risk for substance abuse and other adverse outcomes. Internet-based intervention offers significant potential as part of a population-wide strategy for bringing evidence-based parenting practices to a broad range of parents experiencing challenges in raising their children. Furthermore, pediatricians could be a natural touchpoint for reaching families with evidence-based parenting supports. The field knows little, however, about the potential of the internet to strengthen parenting practices, or about how pediatric practitioners might be engaged in improving the reach of an online parenting program. This study will experimentally evaluate an internet-based version of the Triple P Positive Parenting Program, the Triple P Online System (TPOS), which presents the Triple P content in an interactive, video-enriched, and personalized format with 3-levels of flexible dosage, and will compare it against usual community services. Thirty pediatric clinics involving 100 practitioners in 9 counties across western Washington will be recruited and randomized to receive (a) access for their patients to the Triple P Online System and training in how to effectively promote TPOS and advise parents on their children's behavior problems or (b) Usual Care Community-Waitlist Control, in which parents will be assisted with an appropriate referral for services in the community. Practitioners will recruit into their respective conditions 400 families of 3-8 year-old children with elevated behavior problems. Measures of parents' parenting practices, family functioning, children's disruptive behavior problems, and practitioners' protocols for advising on behavior problems will be obtained at baseline, post-intervention, and 1-year follow-up. The efficacy of the Triple P Online System in improving these outcomes will be examined, as well as dosage-response relationships. This study will further our understanding of the potential value of promoting internet-based parenting programs through pediatric practitioners. Maximizing the reach of evidence-based parenting programs has the potential to reduce the prevalence of children's behavior problems, and thus reduce risks for later problems such as substance abuse.