This study examines the effects of student-, family-, and school-related factors on student achievement at lower secondary schools in rural Cambodia. To investigate the determinants of student achievement, a survey study was conducted in four rural districts, including 20 lower secondary schools for investigation. A total of 517 seventh graders were randomly selected for the study. Questionnaires and achievement tests were utilized as tools for data collection. Due to the nested and hierarchical structure of data, a two-level hierarchical linear model was employed to assess what factors may have affected student achievement. The results indicated that absenteeism and private-tutoring attendance significantly affected student achievement. The negative effect of absenteeism has highlighted the critical roles of parents, teachers, and related educational stakeholders to ensure that students come to school on a regular basis. Despite the positive effect on achievement, private tutoring has greatly disadvantaged Cambodian students from financially disadvantaged backgrounds. In contrast to some existing findings, significant effects were not found among family and school factors. The findings make up the empirical evidence needed for the development of improved education policy and practice in Cambodia.