Multi-tiered systems of support (MTSS) is a framework for providing high-quality academic instruction and behavioral interventions matched to student needs at multiple levels, monitoring progress frequently to assess whether instruction or goals should be adapted, and using data to solve problems and make important educational decisions.
Batsche, Elliott, J., Graden, J., Grimes, J., Kovaleski, J., Prasse, D., et al. (2005). Response to intervention: Policy considerations and implementation. Alexandria, VA: National Association of State Directors of Special Education.