The purpose of this article is to describe preliminary psychometric characteristics of a student self-report measure of self-determination, the Self-Determination Inventory: Student Report version (SDI-SR), designed for youth with and without disabilities. We administered the draft assessment to 311 youth and examined item functioning using structural equation modeling and item response theory. The 50 items that demonstrated strong psychometric properties were examined for construct validity using a series of confirmatory factor analyses. Overall, the pilot measure aligned well with the theoretical framework that guided its development, demonstrating acceptable model fit in adolescents with and without disabilities. Implications for further development and practice are discussed.