LST is currently the most extensively evaluated schoolbased prevention approach available. More than two decades of research have demonstrated prevention effects with respect to tobacco, alcohol, and marijuana use; multiple substance use; and illicit drug use; as well as hypothesized mediating variables. The magnitude of the reported effects typically has been large, with most studies demonstrating initial reductions of 50 percent or more relative to the control groups. These studies have generally produced reductions in both occasional (i.e., experimental) ATOD use and more serious levels of substance use. Studies of the LST
approach have tested its short-term effectiveness, its long term durability, and the use of different delivery methods as well as the effectiveness of booster sessions, its effectiveness when conducted by different program providers, and its effectiveness with different populations. These studies have ranged from small-scale pilot studies involving two schools and a few hundred adolescents to large-scale, multi site,randomized field trials involving more than 50 schools and several thousand adolescents