Social, emotional, and behavioral problems present many issues and concerns for youth, families, and schools. Schools have adopted various frameworks of prevention and intervention meant to assist with such concerns. Two widely used frameworks are positive behavioral interventions and supports (PBIS) and social-emotional learning (SEL). The purpose of the present study was to examine the effectiveness, implementation fidelity, and social validity of an integrated approach (PBIS + SEL) at Tier 2 in relation to students' prosocial classroom behavior. This was done using a common PBIS intervention, check-in/check-out (CICO), in conjunction with a common SEL intervention, mindful breathing (MB). Results suggest that CICO and CICO + MB may both be effective, feasible, and socially valid strategies for increasing prosocial classroom behavior and reducing externalizing and internalizing behavior problems in youth. More specifically, the MB component may produce small but additional valued outcomes compared to CICO alone. Future research should further investigate this value-added effect of MB when used with CICO for social, emotional, and behavioral outcomes as well as other possible methods of integration at Tier 2.