The Student Orientation to School Questionnaire (SOS-Q) is a multidimensional student-centered assessment tool for measuring psychosocial facilitators of student engagement. The SOS-Q is based in research on the self-system models of motivation and direct student input on perceived supports and barriers for high school completion. The current study examined internal measurement properties (factor structure and reliability) of the upper-elementary and high school versions of the SOS-Q in two samples of Grade 4 (N = 615) and Grades 7 and 9 (N = 1,356) students, as an important step in the process of scale development and validation. Exploratory and confirmatory factor analyses (EFAs and CFAs) converged on a stable and reliable measurement structure for both versions of the scale, with common factors related to safe and caring school, peer relationships, self-confidence, external and internal resilience, and for the high school version only--perceived utility of school and extracurricular activities. Results are discussed in terms of incorporating the SOS-Q into comprehensive school assessment systems that go beyond the academic achievement and behavioral data and that can have important policy and program implications. (Contains 4 tables and 1 note.)