Two prominent factors that have been linked to students' mathematics achievement are teachers' instructional practices and students' self-efficacy. However, these factors are typically considered in isolation, negating the relationship between the two. This study examined the effect of two instructional practices, direct instruction and inquiry learning, on elementary students' mathematics achievement, and how students' self-efficacy beliefs mediate this relationship. The study further investigated whether such relationships are moderated by students' Individual Education Plan (IEP) status. Data from standardized math tests administered to grade 6 students and questionnaires administered to students and teachers were analyzed in a multilevel factor score path analysis. Results demonstrated an indirect effect of instructional practice on math achievement through its influence on students' self-efficacy. Specifically, inquiry learning was positively associated with students' self-efficacy, whereas direct instruction was negatively associated with self-efficacy. Further, results showed a direct effect of inquiry learning on math achievement, but only for students with IEPs.