The present study evaluated the effectiveness of an instructional intervention (schema-based instruction, SBI) that was designed to meet the diverse needs of middle school students by addressing the research literatures from both special education and mathematics education.Specifically, SBI emphasizes the role of the mathematical structure of problems and also provides students with a heuristic to aid and self-monitor problem solving. Further, SBI addresses well-articulated problem solving strategies and supports flexible use of the strategies based on the problem situation. One hundred forty eight seventh-grade students and their teachers participated in a 10-day intervention on learning to solve ratio and proportion word problems, with classrooms randomly assigned to SBI or a control condition. Results suggested that students in SBI treatment classes outperformed students in control classes on a problem solving measure, both at posttest and on a delayed posttest administered four months later.However, the two groups' performance was comparable on a state standardized mathematics achievement test. KEYWORDS: word problem solving, ratio and proportion, middle school students, schema- One of the major difficulties noted in this domain is that students tend to use additive rather than multiplicative solution methods (e.g., "to solve 6:14 = ?:35, they find the difference between 6 and 14 and subtract it from 35 to find 27:35 rather than seek multiplicative relationships," Fuson & Abrahamson, 2002, p. 213). Research in this domain has examined how children reason in various proportionality tasks and the extent to which developmental or SCHEMA-BASED INSTRUCTION 4 instructional factors influence proportional reasoning (e.g., Bright, Joyner, & Wallis, 2003;Lamon, 1993Lamon, , 2002Lo & Watanabe, 1997;Post et al., 1988). Proportional reasoning develops over time and "understanding at one level forms a foundation for higher levels of understanding" (Lamon, 2007, p. 637). Recommendations outlined in the research for developing children's proportional thought processes have included providing ratio and proportion tasks in a wide range of contexts (e.g., measurements, prices, rates) and ensuring that students have experienced conceptual methods before presenting symbolic methods such as cross-product algorithm for solving proportional problems (Lamon, 1999;Van de Walle, 2007).The topics of ratio and proportion are frequently encountered in elementary and middle schools in the form of word problems. Traditionally, word problems are used to teach "mathematical modeling and applied problem solving" (Van Dooren, De Bock, Hessels, Janssens, & Verschaffel, 2005, p. 58). That is, the word problem context provides a description of a problem-solving situation that requires responding to a question by executing "one or more operations (+, -, x, ÷) on the quantities in the problem" (Van Dooren et al., 2005, p. 58).However, word problem solving has proved to be a significant challenge for students, in part because it requires s...