Historically Black Colleges and Universities (HBCUs) have been studied consistently as a single institutional group. However, at least ostensibly, HBCUs are relatively heterogeneous. Consequently, we evaluated the homogeneity of three educational outcomes that have been recognized as potentially distinguishing features of HBCUs (i.e., STEM major, GPA, and degree completion). Hierarchical linear and nonlinear modeling conducted on two large databases suggested greater variability within HBCUs than between HBCUs. This variability tended to be explained by HBCUs' public versus private status, advanced degrees offerings, and enrollment. We conclude that HBCUs' institutional characteristics are relevant, but that they may underscore differences within one institutional group.