["Journal of Applied Research in Intellectual Disabilities, Volume 39, Issue 4, July 2026. ", "\nABSTRACT\n\nBackground\nPromoting self‐determination during adolescence is crucial for enhancing academic engagement and social inclusion. This study examined the effects of the Self‐Determined Learning Model (SDLMI) on the self‐determination of students with and without intellectual disability (ID).\n\n\nMethods\nA randomised parallel‐group trial involved 90 adolescents aged 13–17 years (M = 14.05, SD = 1.39), including students with (n = 41, 45.6%) and without ID (n = 49, 54.4%). Participants were randomly allocated to either the experimental (n = 41) group—which received the 12‐week SDLMI intervention or the control group (n = 49), which followed standard school activities. Total composite self‐determination scores and its components‐constructs and essential characteristics were assessed pre‐ and post‐intervention using the Self‐Determination Inventory: Student Report (SDI:SR).\n\n\nResults\nLinear mixed‐effects models were employed as the primary inferential analysis to examine Group × Time interaction effects. Baseline equivalence between groups was confirmed. Linear mixed‐effects modelling revealed significant effects for the total composite self‐determination score, demonstrating significantly greater improvements in the experimental group compared to the control group. Improvements were particularly evident in components‐construct of autonomy (p = 0.001, d = 0.89) and self‐realisation (p = 0.05, d = 0.56). Effect sizes indicated small‐to‐moderate gains, suggesting significant but incremental changes over the intervention period. No statistically significant changes were observed in the control group.\n\n\nConclusions\nThe findings provide robust evidence for the causal efficacy of SDLMI as a viable instructional framework to foster self‐determination skills for students with and without ID in mainstream inclusive classrooms.\n\n"]