This research study is a mixed-methods quantitative and qualitative study that analyzed data from an intensive, long-term professional development project named, "Project: Making Mathematics Matter. (PM[superscript 3])" carried out in two low-performing, high-poverty districts. Two of the districts served as treatment districts and ALL teachers (general education, special education, ELL) who taught mathematics to students in grades 4-8 participated in a four-year PM[superscript 3] mathematical intervention. Three elements identified in the research as effective components in mathematics professional development served as foundational for this project. They were: teachers attended monthly institutes focused on deepening the pedagogical, content knowledge for teaching mathematics; teachers received on-site coaching from an experienced mathematics educator to support implementation of new instructional strategies; and teachers participated in monthly, collegial, grade band meetings facilitated by their coach. This study's analyses focused around three areas: 1. increased pedagogical knowledge for teaching mathematics as measured by the "Learning Mathematics for Teaching" (LMT) assessment (Hill, Schilling, & Ball, 2004); 2. improved mathematics instructional quality as measured by the SAMPI Classroom Observational Protocol; 3. increased mathematics performance of students as measured on the state-wide MEAP test. Research findings were: 1. LMT data collected at the beginning, middle, and end of PM[superscript 3] showed treatment teachers significantly increased their pedagogical, content knowledge for teaching mathematics over their matched-comparison teachers; 2. Analyses of SAMPI data demonstrated teachers significantly improved the quality of their classroom instruction; 3. Analyzing sets of MEAP student scale scores by grade and year, there was a significant interaction between district of the student and the year, during and following treatment teachers' participation in PM[superscript 3]. Where in 2005, all sets of treatment scale scores were significantly different and lower than comparison scores, as the years of treatment teacher participation in PM[superscript 3] increased many sets of compared sets of MEAP scores were no longer significantly different. This study suggests a connection between the increased content knowledge of teachers, the improved quality of classroom instruction, and the increased mathematics achievement of their students in high-poverty, low-performing districts. [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.]