This study adopted a cross-sectional and correlational research design in an attempt to add our understanding of student- and teacher-level factors that help explain variability in students' science achievement to the existing literature. More specifically, the present article examined students' science achievement in relation to their constructivist learning environment perceptions, epistemological beliefs, and self-regulation as well as their science teachers' characteristics. Data were gathered from both 137 science teachers and their 3281 seventh grade students via administering self-report questionnaires. Hierarchical linear modeling (HLM) analysis was conducted to analyze the two-level data (student level and teacher level). Students' learning environment perceptions, epistemological beliefs, achievement goals, and self-regulation constituted student-level data while teachers' self-efficacy, achievement goals, and epistemological beliefs constituted teacher-level data. The findings indicated that students' constructivist learning environment perceptions were significant predictors of their science achievement. Additionally, students with sophisticated epistemological beliefs appeared to be more successful in science. Also, performance avoidance goals were negatively related to science achievement. Among teacher-level variables, teachers' self-efficacy and sophisticated epistemological beliefs were found to be positively linked to students' science achievement.