A three-tier model for increasingly intense academic and behavioral interventions. The percentages represent estimates of the number of children who are at grade level (Tier 1) and who require Tier 2 and Tier 3 services. Note. From Response to Intervention: Policy Considerations and Implementation (p. 22), National Association of State Directors of Special Education, Inc., 2006, Alexandria, VA: Author. Copyright 2006 by the National Association of State Directors of Special Education, Inc. Reprinted with permission.