MTSS, or Multi-Tiered System of Supports, is a proactive framework of tiered instruction and support for all students. We think about MTSS as a triangle with three “tiers.” Every student in a school will fall somewhere on the MTSS triangle—either Tier 1, 2, or 3. MTSS is not a curriculum or program, but a way to think through how to best intervene and provide resources and interventions for students who are struggling with reading, math, or behavior. (Source)