Continued tuition increases intensify the pressures to ensure learning and academic growth in undergraduate education is happening and reinforce the need for critical assessment of factors impacting student performance. Class size is one factor that may impact course outcomes and student academic growth. The purpose of this study was to determine if class size in an introduction to sustainability course affected students’ ecological worldview upon completion of the course. Post-test New Ecological Paradigm (NEP) results indicated that all class sections had positive increases in mean scores ranging from 60.2 + 9.4 for the 49-student section to 61.6 + 5.4 for the section with 39 students. An ANCOVA between the three sections (class size of 39, 49, and 60) revealed a non-significant (P = 0.153) main effect for class size. The estimated marginal mean for section sizes were n = 39 (62.1), n = 49 (59.6), and n = 60 (60.9), respectively. Results of this study indicated that class sizes of 39, 49 and 60 did not contribute to any differences in students’ ecological worldviews. The authors recommend additional research on multi-section courses with larger student numbers to determine when class size would impact a course that emphasizes active learning.