This dissertation examines the co-requisite support structure for entry-level mathematics as applied to STEM-bound students, those students who have declared a STEM major but have been deemed underprepared for entry-level mathematics by Texas Success Initiative standards. Using data from a very large community college in Texas, the first study found STEM-bound students differed from STEM students (students who passed Calculus with a C or better) with prior developmental mathematics (DM) by race/ethnicity, sex, and socioeconomic status, suggesting systems and mechanisms in place to reach Calculus served to reduce the diversity present among STEM-bound students. The study also found that STEM students with prior DM navigated 13 different course sequences within four main sequences before successfully completing Calculus. DM grade point averages were significantly different between the main sequences. The second study utilized propensity score matching to compare: (1) a control group of STEM-bound students enrolled in Elementary Algebra to a treatment group of STEM-bound students enrolled in co-requisite College Algebra (CA) and (2) a control group of students enrolled in Intermediate Algebra to a treatment group of STEM-bound students enrolled in co-requisite CA. After matching, enrolling in co-requisite CA was associated with higher odds of completing DM, earning CA credit, and persisting along the path to Calculus compared to enrolling in Elementary Algebra. There was no statistically significant difference in outcomes for students enrolled in co-requisite CA compared to Intermediate Algebra. The last study utilized generalized hierarchical linear modeling to examine the impact of co-requisite CA course design on student outcomes. The model examined two different course designs: (1) a redesigned CA course with just-in-time (JIT) remediation and (2) a traditional CA course with an emporium lab. The study found that the JIT model increased the likelihood that STEM-bound students completed DM requirements, earned CA credit, and persisted along the path to Calculus, compared to the emporium model, controlling for Level-1 and Level-2 covariates. These findings have practical implications for practice as colleges across Texas are scaling up the use of co-requisite support for STEM-bound students. The studies also create a framework for additional research into this emerging DM intervention.