Autonomous functioning, an essential characteristic of self-determined people, has been categorized behaviorally according to everyday activities in Self & Family Care (SFC), Life Management (LM), Recreation/Leisure (RL), and Social/Vocational (SV) skills. The effectiveness of a short-term (8-10 weeks) educational residential program to improve skills in these categories of everyday activities in adolescents with intellectual and developmental disabilities was examined, and the effect on participant self-determination was also measured. Results from this single-group, quasi-experimental research with three data collection points (n = 31 from five cohorts over an 18-month period) found that participants' skills in SFC/LM and RL had improved significantly with large effect sizes at postprogram and 3-month follow-up. Skills needed for SV activities did not show the same level of improvement, but participant-rated self-determination scores (as measured by the AIR Self-Determination Scales) improved significantly with small effect size at postprogram and moderate effect size at follow-up. (Contains 3 tables and 2 figures.)