This study examined the impact of the levels of fidelity of teacher implementation of a research-based middle school mathematics program, implemented systemically across a district, on student achievement benchmarks. By examining the systemic implementation based on the level of fidelity to the written curriculum, this quantitative study sought to determine whether there was a statistically significant relationship between the level of fidelity of teacher implementation for the intended middle school curriculum and two different student achievement benchmarks in Algebra I in grade nine. The middle school mathematics program used in the study, Algebraic Thinking, was designed as a three-year series of courses for students in grades six, seven, and eight, constructed specifically to prepare them for Algebra I in the ninth grade. It was implemented systemically in all 27 comprehensive middle schools across the school district studied. Secondary data used for this research included student state test scores for the Maryland High School Assessment (HSA) for Algebra and Data Analysis administered during the 2009--2010 and 2010--2011 school years along with the Algebra I final grades from this same set of ninth-grade students. These ninth-grade students in Algebra I had been taught with the Algebraic Thinking program for two or three years before entering Algebra I. In addition, the middle schools these students attended all received fidelity ratings for their implementation of the Algebraic Thinking mathematics program. These fidelity ratings were used as part of the study. The data sets were analyzed to determine if there was a relationship between the level of fidelity of implementation of the Algebraic Thinking middle school mathematics program and student performance on the HSA as well as final grades in Algebra I. The results from this study showed that there was a significant relationship between the level of fidelity of teacher implementation to a research-based middle school preparation program and student performance in Algebra I as well as on a state assessment. This study provided evidence of how the level of fidelity of an implementation by middle school teachers across a school district of a research-based algebra preparatory program impacts the performance achievement of individual students as well as of an entire school system. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]