Comparison is a powerful tool that has been shown to improve learning in a variety of domains. In both laboratory studies and small-scale classroom studies, having learners compare and contrast worked examples has been shown to reliably lead to gains in students' knowledge. Comparison is also integral to "best practices" in mathematics education. Having students share solution procedures for a particular problem and then discuss the similarities and differences in the different procedures lies at the core of reform pedagogy in many countries throughout the world. Researchers' past empirical work has illustrated the potential benefits of comparison for students' learning of mathematics. Students who were shown two worked examples side-by-side and given the opportunity to compare and discuss similarities and differences between problems, solutions, and strategies achieved greater gains in conceptual knowledge, procedural knowledge, and flexibility, as compared to control students. The current intervention sought to build upon past research by scaling up materials to encourage comparison in the classroom throughout the academic year using a randomized control trial design. This report provides the results of a year-long experiment examining the impact of researcher-designed supplemental curriculum materials that "infused" comparison into the learning and teaching of Algebra I. The question guiding this research is as follows: What is the effect of the supplemental comparison curriculum on Algebra I students' knowledge? Data were collected from teachers and students in 57 public schools across the state of Massachusetts during the 2010-2011 school year. Suburban, urban, and rural schools were represented. Results suggest that, when implemented with sufficient dosage and instructional quality, use of the supplemental curriculum that "infused" comparison into the learning and teaching of Algebra I improved students' learning of mathematics. Future research will determine whether encouraging sufficient dosage and instructional quality of this supplemental curriculum in classrooms might lead to better student outcomes than business-as-usual classrooms. Tables and a figure are appended.