Students vary in their perceptions of teachers' motivational supports, even within the same classroom, but it is unclear why this is the case. To enable the design of equitable environments and understand the theoretical nature of motivational climate, this study explored demographic differences in university students' perceptions of instruction across five large, introductory STEM (science, technology, engineering, and mathematics) courses (N = 2,486), along with end-of-semester outcomes. Results indicated that women and students from traditionally underrepresented racial or ethnic groups (Black, Hispanic/Latino/a, or Indigenous students) tended to perceive slightly higher motivational support in their courses compared to men and traditionally overrepresented (White or Asian) students, respectively. However, patterns were not uniform across all courses or variables. Men and women did not significantly differ on end-of-semester interest in any course, but women tended to have lower self-efficacy in some courses and significantly higher grades in programming compared to men. Implications include a caution for researchers against interpreting sample-specific or aggregated evidence of demographic differences as generalizing to broader populations or specific settings.