Research in the field of intellectual disability suggests that promotion of self-determination triggers positive transition outcomes for youth with intellectual disability. This article examines the contributions of personal and environmental variables in predicting self-determined action in students with and without intellectual disability. The Spanish pilot versions of the Self-Determination Inventory and the AIR Self-Determination Scale were administered to 114 youth with and without intellectual disability. Personal and environmental variables were treated as predictor variables for analytic purposes. The results indicate the relevance of environmental variables in predicting both self-reported capacity for self-determination and the essential characteristics of self-determined action. Particularly, age and opportunities at school and at home to engage in self-determined action played a significant role. The practical implications of these findings and suggestions for future research are discussed.