At our Historically-Black University, about 89% of first-year students place into developmental mathematics, negatively impacting retention and degree completion. In 2012, an NSF-funded learning enrichment project began offering the introductory and developmental mathematics courses on-line over the summer to incoming science, technology, engineering and mathematics (STEM) majors at no cost to students. Passing rates for the summer on-line classes were around 80%, and students in the on-line classes scored equivalently on the common departmental final exams as students taking the classes in the traditional format. For students who passed the on-line classes, their performance in the following classes (College Algebra and Trigonometry) at least equaled that of students who progressed to those courses by taking the traditional series of in-person courses. Three years of data show that students who started college with an on-line mathematics course in a summer bridge program had a higher first year GPA, a better first year retention rate and earned significantly more credits in their first year than the overall population of STEM students. While not solely attributable to the on-line classes, these results suggest that offering introductory mathematics courses on-line as part of a freshman bridge program is an effective, scalable intervention to increase the academic success of students who enter college under-prepared in mathematics. The positive results are particularly exciting since the students in our project were 87% minority.