The purpose of this study was to explore the cross-cultural validity of the Self-Determination Inventory: Student Report, a newly developed measure of self-determination grounded in Causal Agency Theory. The tool was translated to Spanish and administered to American and Spanish adolescents. The sample was structured to include adolescents with and without intellectual disability in both cultural contexts. More than 3,000 students in the U.S. and Spain aged 13 to 22 completed the assessment. Findings suggest that the same set of items can be used across cultural contexts and in youth with and without intellectual disability, although there are some specific differences in item functioning across students with and without intellectual disability in Spain that must be further researched. There were specific patterns of differences in latent self-determination means, with students with intellectual disability scoring lower in the U.S. and Spain. Implications for assessment research and practice in diverse cultural contexts are explored.