This study examined the internal structure of the Scales for Assessing Emotional Disturbance-3 Rating Scale (RS), a teacher-completed RS developed to measure emotional disturbance (ED). As defined in U.S. law and regulations, ED involves five characteristics or patterns of behavioral and emotional maladaptation. RS data obtained on a sample of students with ED were used to examine validity evidence based on the internal structure of the assessment. Of particular interest was the extent to which multivariate factors derived from the RS data conform to the five characteristics of ED stated in the definition. Results indicate that the RS data fit a 5-factor model reasonably well. A subsequent bifactor analysis identified a considerable proportion of common variance across factors, suggesting the presence of a strong general ED factor, two distinct group factors (Inability to Learn and Inappropriate Behavior), and three weak group factors. The findings provided evidence of the validity of the SAED-3 RS based on internal structure and pointed to support for use of the RS in contributing to the process of determining whether a student qualifies for the ED education disability. Implications for improved research on the nature of ED and how students with ED can be better served are discussed.