Response to Intervention (RtI) - an approach to the early identification and support of students with learning and behavior needs. RtI mandates the use of research-based academic and/or behavioral interventions. RtI includes universal screening of all children and generally includes three tiers of instruction. Tier 1 is high-quality, code-based classroom instruction. Tier 2 is targeted supplemental instruction for students not making adequate progress in the regular classroom. Tier 3 is intensive, targeted intervention for students not making adequate progress in Tier 2. Students who do not achieve the desired level of progress in response in Tier 2 or Tier 3 intervention are referred for a comprehensive evaluation and considered for eligibility for special education services. Multi-Tiered System of Support (MTSS) is a term related to RtI. Sometimes the terms are used interchangeably, but the approaches differ in several ways. Among several distinctions between the two approaches is that MTSS emphasizes a system-wide responsibility for student support at all grade levels and throughout the district or state. Meanwhile, RtI can be implemented at any level (classroom, grade, school, district).