The concept of academic momentum links student enrollment patterns to degree completion whereby patterns of meaningful, consistent collegiate enrollment increase the likelihood of earning a degree. Academic momentum encompasses both a student's trajectory and rate of progress toward a tangible academic outcome with a core assumption that momentum is established very early in a student's academic career: typically, through full-time course loads during the student's first few semesters, direct transitions from high school to college, and enrollment in the summer sessions leading into the fall of the student's first year. Interventions designed to energize first year academic momentum are consistently shown to improve students' likelihood of completing credentials generally, and among members of historically underrepresented groups in particular. Research in this area typically focuses on identifying elements that establish good momentum. This study, in contrast, focuses instead on an institutional factor, class availability, and how it influences changes in momentum over time. Specifically, I proposed that academic momentum is constrained by the availability of classes at the institution, and that students' momentum is directly impacted by the availability of certain types of classes over others. I hypothesized that course availabilities and the significance of an enrollment in more or less available disciplines would depend on the general goal of students enrolled at the school, as exemplified by their general course-taking and enrollment behaviors over their first couple of years. Multilevel growth modeling techniques were used to the study changes in academic momentum within students over a six-year period. Seven multilevel growth models, in total, were used in this study. Following standard practice, the models first established the appropriateness of multilevel growth modeling techniques before subsequently examining trends in momentum over time, accounting for differences due to student demographics, and eventually looking at offerings by subjects and the effects of enrollment in those subjects on academic momentum. The final set of models confirmed that course offerings in two disciplines, math and English, both had an effect on academic momentum beyond students' demographics and enrollment trajectories. Specifically, more math course offerings greatly accelerated academic momentum among students while more English course offerings moderately slowed momentum down. Neither of these effects were contingent on enrolling in the discipline, meaning that students were affected by additional English and math course offerings regardless of whether they were enrolled in either English or math, respectively. This study demonstrates that multilevel growth models can serve as an important tool for understanding academic momentum beyond traditional approaches such as piecewise regression models, which segment unit loads and potentially overemphasize the importance of course taking in a students' first year. Treating academic momentum in a more flexible way allows researchers to consider factors beyond the student's control that subtly affect their rate of progress through school. The results emphasize the importance of considering how instructional resources are allocated in relation to student success, and what courses and their availability represent to students who either do or do not enroll in a particular course. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]