Students with mathematics learning disabilities have a weak understanding of mathematical concepts that underlie success in Algebra I, such as ratios and proportional reasoning. In this study, researchers used a multiple baseline across participants design to evaluate the effects of a intervention based on a instructional trajectory of how students come to understand ratios through build-up, emergent unit, and unit strategies on performance on a test of ratio equivalence. Student performance during intervention indicated a functional relationship between the instruction and higher scores on a curriculum-based measure across three students. Student use of increasingly sophisticated strategies over the course of the intervention also increased. Results as well as possible implications and future research are discussed.