In this mixed methods study, we used a state-wide survey to explore the perceptions of 936 preschool through second-grade teachers about inclusion in their elementary school's social-emotional multitiered system of supports (MTSS). Overall, early childhood teachers reported feeling included in their school's social-emotional MTSS. Results of a one-way between-subjects analysis of variance (ANOVA) indicated that preschool teachers working in elementary schools reported general agreement about being included, but not as strongly as kindergarten, first-, and second-grade teachers. Qualitative analyses of teachers' open-ended responses revealed similar grade-level patterns. When early childhood teachers did not feel included, they described feeling separate from the rest of the school, using a different social-emotional approach, or the school's social-emotional MTSS approach not being appropriate for their students. Inclusion in school-wide activities and implementation issues, such as consistency across teachers, an efficient behavioral MTSS process, and training opportunities, affected teachers' feelings of inclusion in the social-emotional MTSS.