To examine a) the feasibility of delivering a summer treatment program for pre-kindergarteners (STP-PreK) with externalizing behavior problems (EBP) and b) the extent to which the STP-PreK was effective in improving children's school readiness outcomes. Participants for this study included 30 preschool children (77 % boys; Mean age=5.33 years; 77 % Hispanic background) with at-risk or clinically elevated levels of EBP. The STP-PreK was held at an early education center and ran for 8-weeks (M-F, 8 a.m.-5 p.m.) during the summer between preschool and kindergarten. In addition to a behavioral modification system and comprehensive school readiness curriculum, a social-emotional curriculum was also embedded within the STP-PreK to target children's self-regulation skills (SR). Children's pre- and post-school readiness outcomes included a standardized school readiness assessment as well as parental report of EBP, adaptive functioning, and overall readiness for kindergarten. SR skills were measured via a standardized executive functioning task, two frustration tasks, and parental report of children's emotion regulation, and executive functioning. The STP-PreK was well received by parents as evidenced by high attendance and satisfaction ratings. Additionally, all school readiness outcomes (both parent and observational tasks) significantly improved after the intervention (Cohen's d effect sizes ranged from 0.47 to 2.22) with all effects, except parental report of emotion regulation, being maintained at a 6-month follow-up. These findings highlight the feasibility and utility of delivering an early intervention summer program that can successfully target multiple aspects of children's school readiness, including behavioral, social-emotional/self-regulation, and academics. (author abstract)