The Common Core State Standards for Mathematics highlight the importance of not only content standards for mathematics but also mathematical practices such as communication, representation, and reasoning, skills that are often difficult for students with autism spectrum disorder (ASD). Through a single-case multiple-probe-across-participants design, this study found modified schema-based instruction (MSBI) to be an effective strategy to increase the use of mathematical practices for middle school students with ASD when solving multiplicative word problems. Four students eligible for special education services under the area of autism enrolled in sixth-grade general education mathematics classes increased their use of mathematical practices for two problem types (multiplicative comparison and proportion) and maintained the use of mathematical practices 4 to 8 weeks after intervention. Additionally, all participants generalized their use of mathematical practices to novel multiplicative comparison problems containing extraneous information, and three of the participants generalized mathematical practice skills to proportion problems containing extraneous information. Implications for practice are discussed.