The assessment of Intellectual Disability (ID) under the Individuals With Disabilities Education Improvement Act 2004 (IDEIA; Public Law 108-446, 2004) requires the measurement of both intelligence and adaptive behavior (i.e., conceptual, social, and practical skills). This study expands past research by examining current state special education guidelines based on IDEIA and their alignment with best practices in assessment across all U.S. states and the District of Columbia (DC) for the assessment of ID. Aggregated and disaggregated data pertaining to special education guidelines and recommendations are examined, including cut-scores and confidence intervals, information specific to composite adaptive behavior scores versus domain scores, and multiple informants.