Calculus is a stepping stone to science, technology, engineering, and mathematics (STEM) degrees and careers, but countless college students abandon their STEM ambitions after an encounter with calculus--or to avoid taking the intimidating course altogether. While traditional approaches have focused on prerequisite courses--which often repeat high school coursework in algebra, precalculus and trigonometry--research has increasingly called that strategy into question. Cultivating a talented and diverse STEM workforce requires addressing these issues of attrition in students' pathways to STEM, attrition that disproportionately affects women and minoritized students. This report analyzes how the California State University (CSU) system structures its Calculus prerequisite sequences across 23 campuses and the impact of these courses on student attrition. Through an in-depth analysis of CSU prerequisite sequences and interviews with math leaders at eight CSU campuses, the authors uncover long on-ramps to Calculus, confusing pathways, a heavy reliance on placement testing, and varying systems of student support. Recommendations for education system leaders and policymakers emerging from this report include further research to ensure that campuses' prerequisite approaches are effective in promoting success in Calculus and in STEM fields. Campuses, systems, states, and funding agencies should support the use of student-level data to analyze and disaggregate outcomes to shed light on the effectiveness of various practices for students generally, and especially for historically excluded groups. [Additional funding provided by Valhalla Foundation.]