The objective of this study was to evaluate two early intervention packages to promote successful transitions to kindergarten for preschoolers with behavior problems recruited from Head Start preschools. Fifty children (M_age = 61 months; 76% male; 98% minority) referred by teachers due to early externalizing behavior problems were randomly assigned to one of the two groups. Group 1 (high intensity; HI) received a 4-week intensive summer program before the start of kindergarten, weekly parent workshops, and monthly school consultation and parent workshops throughout kindergarten. Group 2 (low intensity; LI) received only parent workshops. Program feasibility, child improvement, and parental satisfaction data were collected along with parent and teacher reports and measures of school readiness. Children in the HI group demonstrated fewer problem behaviors and less student–teacher conflict as reported by teachers. Early intensive summer interventions prior to kindergarten were found to be a promising avenue to promote successful transitions to school for children from Head Start preschools with behavior problems.