Preschool is an important educational setting for child development, and problem behavior is a prevalent barrier within this setting. Preschool teachers have expressed the need for evidence-based classroom management interventions to address problem behavior. Class-Wide Function-Related Intervention Teams (CW-FIT) is an intervention that incorporates social skills training, group contingencies, and reinforcement to address problem behavior within classrooms. This intervention has been found to be socially valid by teachers and children, and effective in increasing children's engagement, decreasing problems/problem behavior in elementary, kindergarten, and first- and second-grade classrooms. The aim of the current study was to evaluate a modified CW-FIT as an effective strategy to address problem behavior within two community preschools in Ireland across three preschool classes with 32 children. A multiple-baseline design across groups was employed to evaluate the outcomes, with measures of generalization and maintenance (for one group) also taken. Visual analysis of data revealed an increase in the children's on-task behavior and social skills as well as a decrease in children's problem behavior within these settings. Generalization (across all three groups) and maintenance (across one group) of these findings for on-task behavior and problem behavior were also observed. Social validity measures showed that teachers rated the intervention as socially acceptable.