Despite widespread efforts to address barriers to college success, low-income and first-generation students continue to complete college at substantially lower rates that their more advantaged peers. A review of causal research to date has linked comprehensive interventions (e.g. programs that provide students with a combination of financial, academic and social support) to promising persistence and degree attainment outcomes for low-income and first-generation students. However, the body of causal research on the impact of these type of interventions remains nascent. This mixed-methods dissertation study contributes to this critical research area by using rigorous quasi-experimental methods to examine the impact of the Dell Scholars Program on the college persistence trajectories of its participants. An earlier regression-discontinuity study revealed large and significant impacts on degree attainment rates. Specifically, the study found that the program has a 9 percentage-point and 16 percentage-point impacts on four- and six-year bachelor's degree completion rates, respectively (Page, Castleman, Kehoe, & Sahadewo, 2017). This work builds off this prior investigation in two important ways. First, I couple difference-in-differences and matching analytic strategies to estimate program impacts for Dell Scholars beyond the selection threshold. I find significant impacts on persistence, degree attainment, stopout rates, and dropout rates. To explore the mechanisms underlying these impacts, I estimate first-difference impact estimates on first-year loan borrowing behavior, academic progress, and academic achievement. I find significant program effects for all outcomes, with notably larger impacts for students enrolled in less selective institutions. In the second part of my study, I move beyond the question of whether the Dell Scholars Program impacts enrollment and degree completion outcomes to address the critical question of "how" the program achieves successful results. I conduct an explanatory case study that draws on interviews with program staff and students, program administrative data, observations and program artifacts. I identify four key program components that drive the observed causal impacts: the program's use of a proactive, data-informed support system that is highly responsive to persistence risk indicators; the program model's flexible, client-focused practices; the program's work environment and staff background; and the implementation of continuous quality improvement strategies. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]