To address limited access to behavioral health services in primary care, we conducted a preliminary effectiveness study of a novel acceptance and commitment therapy group treatment implemented within pediatric integrated primary care (ACT-IPC) using a retrospective cohort study design. Participants included 110 youth referred after psychological evaluation between 2015 and 2019. ACT-IPC was implemented in nine sessions; participants had a variety of primary psychiatric diagnoses and were predominantly White (93%) and female (81%) with an average age of 15.1 (SD = 1.5). Anxiety (d = −0.71) and depression (d = −0.54) symptoms improved significantly, as did psychological inflexibility (d = −0.52). Additionally, up to three individualized treatment goals were established and tracked weekly. These outcomes also improved significantly (d = −.69 to d = −1.42), and the first two goals evidenced the majority of improvement within approximately the first half of treatment. Reliable and clinically significant change was promising on all outcomes, and few iatrogenic effects were observed. Of note, concurrent individual therapy and psychotropic medication were prevalent within the sample and were not associated with improved outcomes. Overall, findings provide preliminary transdiagnostic effectiveness and feasibility of ACT-IPC and represent a positive example of a reticulated contextual behavioral science approach to treatment development.