This study examined validity of the School Function Assessment (SFA) and interrater reliability of occupational therapist and teacher ratings of students' school function. The validity of the SFA was examined using the known-group method in 35 participants in kindergarten through 7th grade attending elementary schools; 15 students with learning disabilities (LD), 11 students with autism, and 9 students with traumatic brain injury (TBI). The SFA criterion scores for the 23 individual scales were clustered into five distinct parts for the validity analyses. Significant differences in SFA scores among the 3 groups of students were found using Kruskal-Wallis analyses ([chi][superscript 2] ranged from 9.28 to 20.55, p less than 0.01). Two discriminant analyses demonstrated high correct classification of students with autism and LD, but showed less accurate classification of students with TBI, indicating that the SFA scores of students with TBI did not fall into a systematic pattern for classification. For the interrater reliability study, 16 students' ratings by their teacher and occupational therapist were analyzed. Intraclass correlations resulted in moderate relationships between teacher and occupational therapist ratings for the average criterion scores for the three main sections of the SFA: participation, 0.70; task supports, 0.68; and activity performance, 0.73. Results of this study are discussed in terms of validity of score interpretation and the reliability of different team members completing the SFA questionnaire. (Contains 6 tables.)