Group-based parent training (PT) is an evidence-based approach for strengthening parenting skills and reducing child behavior problems. However, there has been little research on the social connectedness (SC) formed among PT participants, particularly in low-income communities where parents may be more socially isolated. This study describes SC formed among parents in a group-based PT program implemented in their children's school and its association with changes in child behavior. Using a convergent mixed-methods design, data collection occurred between 2020 and 2022. Parents (n = 97) completed measures of their SC to other parents in their PT group and their child's behavior. Qualitative interviews with a representative subsample of parents (n = 17) were also conducted to understand parents' perceptions and experiences of SC within their PT group. Parents reported high levels of SC (M = 4.45 range = 3.04-5 on scale of 1-5; SD = 0.4). From baseline to postintervention, the number of children with child behavior problems significantly decreased (32.12%, 37.5% behavior intensity and problems, respectively). The magnitude of decline in child behavior problems was significantly related to parents' SC (b = −11.52, p = .02, SE = 4.99). Qualitative data confirmed high levels of SC, which parents linked to improvements in their parenting and children's behavior. Themes focused on the building of connections, committing to a safe space with parents who share similar goals, supporting one another, and gaining connections within the school environment and during the COVID-19 pandemic. Results highlight the potential synergistic effects of SC formed in the context of group-based PT with implications for strengthening parenting skills and children's well-being. Public Policy Relevance Statement Social connectedness is an important construct that has been linked to improved mental and physical health outcomes. Findings from this study highlight the importance of investing in school-based preventive parenting interventions that improve young children's behavioral health and build socially connected parent communities. These investments are particularly needed in low-income, underresourced communities where parents may experience more psychosocial adversity and isolation.