Mathematics education highlights the importance of helping students understand mathematical content and the ability to think critically about mathematics. Mathematical practice standards outline expectations for engaging students in meaningful mathematics activities to encourage a deep understanding of mathematical concepts and content. For some students, however, engagement in mathematical practices may not come naturally, and therefore will need to be explicitly taught. Students with autism spectrum disorder have communication and executive functioning deficits that are likely to decrease their engagement in mathematical practices. A multiple probe across behaviors single-case design was used to investigate the effectiveness of a modified schema-based instructional (MSBI) strategy on the use of mathematical practices of a middle school student with autism spectrum disorder (ASD). The student was taught to solve equal group, proportional, and percent of change word problems using MSBI. Results provide evidence of a functional relation between MSBI and mathematical practices with three demonstrations of an effect. Results from social validity questionnaires also support the importance of the skills taught, along with an observed behavioral change for the student during mathematics instruction in his classroom setting. Implications for teaching and future research are discussed.