The purpose of this report is to compare changes in social skills, problem behaviors, and academic competence for kindergarten or first grade students identified as being at risk for serious behavior problems who received primary, secondary, or tertiary level preventive interventions. Of the 93 participants in this study, 73% were male; 86% were Caucasian, and 65% were characterized as having externalizing behavior problems. A repeated measures analysis of variance indicated statistically significant differences (p less than 0.01) between the groups based on type of intervention received the Self-Control subscale (e.g., controlling temper, responding appropriately to teasing) of the "Social Skills Rating System" (Gresham & Elliott, 1990). School-wide Positive Behavior Support is an effective primary prevention intervention, even for young children with serious internalizing or externalizing behavior problems. (Contains 2 tables and 9 figures.)