Learning Support Services at the University of California, Santa Cruz is intended to aid students--particularly those who are at highest risk of academic failure--to master the required material and succeed in their courses. It includes two primary components: modified supplemental instruction (MSI) and tutoring. This study uses data from administrative records kept by University of California, Santa Cruz on its students' academic experiences in the 2010-2011 to 2013-2014 academic years to examine the extent of utilization of MSI and tutoring, the types of students engaged in these activities, and the role of Learning Support Services in aiding students to improve their course grades, remain in school, and graduate in 4 years. The study addresses gaps in the literature on both supplemental instruction and tutoring by offering a new method to reduce selection bias in comparing participating to nonparticipating students and by focusing on the extent of participation in programs, rather than whether participation occurred or not. Students who participated in MSI and tutoring earned higher course grades when compared with other students and, in the case of MSI, compared with themselves in courses where they did not participate in MSI. Tutoring, but not MSI, was associated with improvements to retention, and neither was associated with improvements to 4-year graduation.