Online learning platforms integrating open educational resources (OERs) are increasingly adopted in secondary education as supplemental resources for teaching and learning. However, students report difficulties sustaining their engagement because of the self-paced nature of OER-supported learning environments. We noted that little attention has been paid to factors related to student perseverance and attrition in the learning environment. Little knowledge about these factors prevents discussion on how to promote OERs as pedagogical tools that complement the formal school curriculum. To address this research gap, we analyzed student- and teacher-level usage data, and demographic information. The purpose was to explore student- and teacher-level factors associated with the duration of student usage in Algebra Nation, an OER-supported online learning platform adopted in many secondary schools. The results revealed that at the student level, student engagement with video lectures, self-assessment, social tools, and additional videos relevant to solved test items significantly predicted student usage duration. At the teacher level, teachers' use of teacher resources was positively associated with student usage duration. An additional analysis of student and teacher total usage time indicated that, compared with heavy users, light and medium users were more likely to discontinue their engagement in the long term if their teachers did not use the platform. Based on our findings, we provide recommendations for promoting student engagement with OER-supported online learning in secondary education contexts. [This paper will be published in "Computers and Education."]