Background: Research on post-secondary training for individuals with intellectual disabilities has generally focused on programs, with little consideration of the structures and mechanisms that give rise to them. This article adopts a critical realist perspective to comparatively analyse and theorise about the contextual structures contributing to the introduction of post-secondary training programs in universities for individuals with intellectual disabilities. Method: Six stages in critical realist explanatory research were followed. They include (1) description, (2) analytical resolution, (3) abduction/theoretical redescription, (4) retroduction, (5) comparison between different theories and abstractions, and (6) concretisation and contextualisation. Results: Historical, socio-political, and educational policy structures and mechanisms, indicated three program typologies: program as niche, as a generalisable prototype, and as an evolutionary response to evolving conditions. Conclusions: By developing explanations about preconditions, the study draws out nuanced sub-types occurring within a single university-based program, theorises on trajectories for success, and lays the groundwork for future empirical and conceptual development.