This study examined whether or not teacher collaboration in professional learning communities, which is a form of professional development, affected student learning in third-grade mathematics. The sample for the study consisted of 120 students (i.e., 60 students for the experimental group and 60 students for the control group). Both schools were small urban elementary schools from a West Tennessee public school district, and each was close in geographic proximity. Each school administered the Discovery Education Assessments each 9-week period in the months of September, November, and February to measure the students' math performance level. An ANOVA test, frequency analyses, and observations were used to analyze data. The tests from the experimental group were significantly higher than the control group. Teachscape data were used to compare the frequency of teaching strategies between the two schools. The data indicated that both schools used similar teaching practices and grouping formats. However, the frequency analyses indicated that the experimental group spent more time teaching at higher levels of understanding according to the Bloom's Taxonomy chart. Therefore, the experimental group differences in the level of instruction exceeded the control group. The researcher discussed the organizational factors, as stated by the teachers, that supported/impeded the development of professional learning communities in their school. Professional learning communities can be incorporated in the school improvement plan to address the math proficiency of the school community, as well as provide professional development among the teachers that affect student learning. [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://www.proquest.com/en-US/products/dissertations/individuals.shtml.]