The chapter “Classroom-Based Services for Adolescents With Mental Health Needs,” in School Mental Health Services for Adolescents, describes a classroom-based three-tiered framework of prevention and intervention that is efficient and cost-effective. A rationale is provided for why the three-tiered framework, typically applied at the school-wide level, is also a good fit for individual classrooms. Following the rationale, the chapter provides details of specific interventions across the three tiers that have solid or emerging evidence for effectiveness in secondary settings. For each intervention, a rationale is provided, followed by specific procedures and strategies for implementation, as well as research to support the effectiveness of the intervention. The chapter ends by discussing broader implementation issues in the form of individual barriers teachers face and larger systemic barriers in secondary school settings.