This article frames racism as a threshold concept and, using qualitative data from written coursework, examines student learning of that concept in a racially diverse college course. The data suggest scaffolding learning and using real-world applications correlate to student mastery of the threshold concept of racism. Findings also suggest that students of color, those who assessed their understandings of issues of race and racism on the first day of class as mixed (rather than expert or weak), those who took the course primarily due to interest, and upperclassmen moved more quickly toward advanced understandings of racism. Qualitative data illustrate that the ways in which the threshold concept was troublesome and transformative varies for students, particularly by race. This study answers the call for more research on the pedagogy of racism as related to the learning experiences of students of color, especially in diverse classrooms.