The primary goal of the Inter-Venture trial is to assess the potential effect of the school-based targeted interventions and collaborative care in the prevention, early detection and reduction of mental health problems, substance misuse and psychosocial difficulties among young people. The secondary goal is to assess the effect of interventions on school performance and whether the interventions can protect cognitive functions that may be negatively affected by early-onset substance use and mental health problems, and promote cognitive development through the prevention of these difficulties.