In an ongoing effort to increase student retention and success in the undergraduate general chemistry course sequence, a fully online preparatory chemistry course was developed and implemented at a large public research university. To gain insight about the efficacy of the online course, an observational study was carried out in which student performance on final exams and performance in the subsequent general chemistry course were compared between the online cohort and a previous student cohort which completed the preparatory chemistry course in a traditional lecture format. Multiple linear regression analyses were used to compare final exam scores and general chemistry course grades between the online and in-person student cohorts, while statistically controlling for incoming student academic achievement. Results from these analyses suggest the fully online course resulted in statistically significant increases in both the preparatory chemistry final exam scores and course grades in the subsequent general chemistry course. Because the retention of less academically prepared students in STEM majors is a historical problem at the institution in which the online preparatory chemistry course was implemented, the analyses also aimed to determine if this at-risk group demonstrated similar achievement relative to the population at large. Notably, it was determined that students with the lowest incoming Math SAT scores appeared to perform better in the online course relative to the analogous group of students in the in-person course. Though the observational nature of this study does not allow for the determination of causality, these results suggest a fully online course can result in improved performance for large populations of students, without resulting in a negative achievement gap for less academically prepared students. The structure and implementation of the online course and the results from the statistical analyses will be described herein.