This study aims to characterize how students enrolled in a test preparation product, ACT® Online Test Prep (AOP), use that product. Following Geiser (2012), Masyn (2013), and Morin (2016), the authors use latent profile analysis (LPA) to identify students' engagement profiles using four engagement measures: activity, time, practice ACT score, and percent correct. Five engagement profiles were identified: Low-Usage/Low-Performance (24%), Low-Usage/High-Performance (7%), Low-Usage/Moderate-Performance (32%), Moderate-Usage/Low-Performance (17%), and High-Usage/ Moderate-Performance (20%). Moreover, female students were less likely to have a Low-Usage/High-Performance profile. The heterogeneity of engagement profiles is discussed in relation to usage and performance as well as potential future research directions. This study is a first step towards understanding how students engage with online programs for preparing for college entrance exams. Understanding variation in test preparation usage can help inform product improvement efforts and guide new users to get the most from their preparation.