||Check-in, Check-Out (CICO) is a Tier 2 behavior evidence based intervention that is typically used to support students who are engaging in problem behaviors. CICO supports students in meeting school-wide behavior expectations by clearly defining behavior expectations, providing positive feedback throughout the school day on their progress toward meeting behavioral expectations, and access to reinforcement if daily point goals are met. Key elements of the CICO intervention that have made it an effective behavior intervention include: (a) regular feedback and reinforcement from teachers, (b) home-school communication, and (c) daily performance data used to evaluate progress. Emerging research suggests that CICO may be an effective intervention to support students who are engaging in internalizing problem behaviors. This study included three fourth-grade students and one sixth-grade student from a suburban elementary school who were at risk for internalizing behavior problems, and employed a single-subject across-participants design to investigate the following research questions: (1) What is the effect of Check-In, Check-Out for Internalizing Behaviors (CICO-IB) on active engagement behaviors of students with internalizing behavior problems in an elementary school setting? (2) What is the effect of CICO-IB on students' internalizing behavior problems in an elementary school setting? and (3) Do teachers, parents, and students consider the CICO-IB intervention acceptable for the treatment of internalizing behaviors? Results indicated that CICO may be effective in improving active academic and social engagement behaviors of students at-risk for internalizing behavior problems. All four students demonstrated an immediate improvement of their Daily Progress Report point percentages from baseline to intervention phase. The findings of this study provide multiple implications for both research and practice, as well as several directions for future research.