Immigrant students are diverse, arriving in U.S. schools with wide-ranging experiences and strengths. Many are classified as English learners (EL) upon arrival and some are enrolled in specialized newcomer programs. As secondary-age immigrant EL-classified students arrive, they are on tightened timelines to graduation while facing intersecting challenges in accessing learning opportunities. In this mixed-methods study, I examine variation in course access for immigrant students arriving in secondary grades in Oregon over multiple years, then synthesize interview responses from eleven educators in six districts describing course placement policies and practices to contextualize the observed variation. I then estimate the impact of newcomer program participation on the likelihood of course enrollment across core content areas using a matching approach. I find that enrollment levels were low in the year of arrival for all core subjects other than math, and secondary-age immigrant EL-classified students identified as Black and Hispanic/Latinx, as well as those eligible for free/reduced price lunch, are enrolled in core classes at lower proportions than their peers not identified with those characteristics. I find that variation in core content access is consistently predicted by students’ initial English language proficiency and having interrupted formal education. Qualitative results suggest that course placement is a process largely governed by informal practices rather than policies, and decisions are shaped by individuals’ perceptions of student readiness and local capacity. Results from the matching analyses indicate that newcomer program enrollment may constrict access to English language arts upon arrival and social studies in later years, although estimates are sensitive to model specifications and matching approaches.