This study analyzes the evolution of supplementary aids and services in special education policy from 1975 to the present. Of specific interest are (a) how and through what institutional processes has the supplementary aids and services interpretation evolved over time? And (b) how are supplementary aids and services integrated into individual education plans across the United States? Drawing on coded individual education plans from states in 11 circuit court areas and through examinations of federal law, reauthorizations, regulations, and court decisions, the major findings reveal that special education policymaking is both messy and nonlinear. The study contributes to policy-making theories in that special education is an incremental sum of decisions from multiple institutions and that regional variation in implementation raises questions for equity. The implications for practice and policy are discussed.