Within an at-risk sample of preschoolers with externalizing behavior problems (EBP), the current study examined the initial promise of a multimodal intervention, the Summer Treatment Program for Pre-Kindergarteners (STP-PreK), in improving parenting outcomes. Using an open trial design, 154 parents and their preschool children (73% male; M  = 5.06 years; 82% Hispanic/Latino background) with at-risk or clinically elevated levels of EBP (57% of which were referred by schools or mental health/medical professionals) completed a baseline and post-treatment assessment. A subsample of 90 families completed a follow-up assessment approximately 6 to 9 months after treatment completion. Parental measures of parenting stress and discipline strategies were collected across all three assessments. Observational data were also collected across all assessments during a 5-min standardized child-led play situation and a 5-min parent-led clean up task. The parenting component of the STP-PreK included a School Readiness Parenting Program (SRPP) of which the behavioral management component was implemented via a Parent-Child Interaction Therapy (PCIT) adaptation (8 weekly group sessions with 15-20 parents in each group, lack of requirement of "mastery" criteria). All parenting outcomes (both ratings and observed) significantly improved after the intervention (Cohen's d mean effect size across measures 0.89) with all effects being maintained at the 6-9 month follow-up. These findings highlight the initial promise of our SRPP's PCIT adaptation in targeting multiple aspects of parenting while yielding comparable parenting skills acquisition compared to traditional individual PCIT.