Open Educational Resources (OER) are regularly adopted, yet questions persist about efficacy. Do OER improve student performance? Research produces ambiguous results, because these are derived from small sample sizes, inadequate efficacy measures, and neglect of interactional effects. We examine the effect of OER on student grades using over 500,000 courses, including 72,000 students during four years (2017-2020), from a community college in the Northeast of the USA. Relying on logistic regression models, we test the probability of passing and passing with the highest grade. Students who participate in OER initiatives have higher odds of both. Concurrently, these odds are affected by demographic and academic factors. The odds of passing are higher in OER classes for students in good academic standing, entry level, face-to-face classes. The odds of passing with a high grade are more nuanced. Minoritized students in advanced level, in-person OER courses are more likely to earn a "B." White students in entry level, online, non-OER courses are more likely to earn an "A." Overall, OER help most students pass up to a "B." However, they fall short of helping select students reach an "A." If OER are to replace traditional textbooks, more efforts are needed for maximal productivity.