U.S. social programs, set up to address important problems, often fall short by funding specific models/strategies ("interventions") that are not effective. When evaluated in scientifically-rigorous studies, social interventions in K-12 education, job training, crime prevention, and other areas are frequently found ineffective or marginally effective. Interventions that produce sizable, sustained effects on important life outcomes tend to be the exception. The Top Tier Evidence Initiative seeks to assist policy officials in identifying interventions meeting the Congressional Top Tier evidence standard, defined in recent legislative provisions as "well-designed randomized controlled trials [showing] sizeable, sustained effects on important outcomes." "Evidence Summary for First-Grade Classroom Prevention Program (Good Behavior Game plus Enhanced Academic Curriculum)" presents a detailed description of The Classroom Prevention Program, a first-grade intervention that combines: (1) the Good Behavior Game--a classroom management strategy for decreasing disruptive behavior; and (2) an enhanced academic curriculum designed to improve students' reading, writing, math, and critical thinking skills. The intervention was evaluated by conducting a randomized controlled trial in high-poverty Baltimore schools. Key findings include: (1) at age 13 reduced initiation of smoking by 26% and of hard drugs by more than half; and (2) at age 19, increased likelihood of high school graduation by 21% and of college attendance by 62%. The Top Tier initiative's Expert Panel has identified this intervention as Near Top Tier. Intervention benefits and costs are discussed.