The increasing demand for computer science (CS) skills underscores the importance of integrating CS education into K–12 curricula to best prepare students for a digitally-driven society. Despite significant progress in expanding access to CS courses, disparities in participation persist, especially among historically underrepresented groups. This study examines the transition from 8th to 9th grade as a pivotal juncture in CS education, analyzing factors linked to 9th-grade CS course-taking among 5,505 students across eight diverse school districts using logistic regression. Findings show that high academic achievers, male students, Asian students, and those with exposure to CS and Algebra 1 in middle school were more likely to enroll in 9th-grade CS courses. Conversely, participation is lower for females, English Language Learners, and students receiving special education services. These results point to persistent barriers to CS participation extending beyond access alone. We discuss practical implications for middle and high schools, emphasizing the need for targeted outreach and early exposure to CS to foster a sense of belonging and applicability of CS. By identify-ing actionable strategies to address participation gaps, this study provides data-driven recommendations for advancing equity in CS education during the critical middle-to-high school transition.