Part-time students have accounted for a significant proportion of rising participation in higher education in many countries. The objectives of this paper are to enrich the empirical literature concerning the inclusion of part-time adult learners in higher education, and to assess the two competing theoretical frameworks that have emerged to explain the international expansion of higher education in recent decades: human capital theory and social exclusion theory. Human capital theorists argue that increasingly complex demands of economies and workplaces have caused the expansion of educational provision. Theorists of social exclusion argue that increasingly intense competition among labour market participants has caused the inflation of educational credentials. This paper uses original, archival research to narrate the history of part-time, degree-credit study at McGill University in Canada. It finds that McGill provided a wide range of part-time study opportunities in the 1920s and early 1930s, resisted the provision of such opportunities from the 1940s through the 1960s, and reinstated extensive part-time study opportunities for adults in the 1970s. While both educational expansion and credential inflation took place at McGill neither human capital theory nor social exclusion theory can fully account for the rise, fall, and re-birth of part-time study for adults. To understand this evolution, more proximate causes, such as institutional politics and government funding models, must be explored. This paper raises important questions for future research, including those relating to gender and equity in the participation of part-time students in higher education. (Contains 2 tables.)