There is a need for more research regarding school-based behavioral mental health services addressing problematic internalizing behaviors. The purpose of this quantitative study was to implement Acceptance and Commitment Therapy (ACT) combined with Check-in/Check-out (CICO) in an alternative educational setting and evaluate its effects on (a) student ratings of symptoms of distress associated with internalizing problems and (b) teacher-observed problem behaviors consistent with internalizing concerns. This study also aimed to determine if the results of the intervention were maintained after the intervention had been faded and withdrawn and if the participants and facilitators found the procedures socially valid, relevant, and feasible for implementation. Single Case Design methodology was used to evaluate effects across three groups of students. Data analysis was primarily conducted through visual analysis. Statistical analyses were conducted to further quantify data overlap and effect size. Results indicated a decrease in risk status for internalizing problem behaviors for all but one of the 8 participants. There were mixed results for student behavior data, subjective units of distress, and feasibility data. Findings from this study suggest that ACT lessons of this nature may be a promising standalone intervention or addition to existing school-based behavioral interventions if proper supports are in place to enhance its feasibility. Due to the unique circumstances surrounding this study, including the ramifications of the COVID-19 pandemic, the political climate in America, and within the context of an alternative educational setting experiencing severe staffing challenges, findings from this study also shed light on the factors that contribute to the feasibility and acceptability of such an intervention. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]