The purpose of this study was to conduct a meta-analysis of dissertation research that examined the implementation of professional learning communities (PLCs) and student achievement in preK-12 schools. An exhaustive search for such unpublished studies was conducted using the following criteria: 1) the studies were available on dissertation data-bases; 2) the studies originated from institutions with the classification of Carnegie Doctoral/Research Universities-Extensive between 1997 and 2012; 3) the studies involved student achievement data from preK-12 schools; 4) the studies included some type of assessment of PLC characteristics and some form of student academic achievement data which were quantitatively linked; and 5) the studies reported the quantitative data necessary to calculate effect size (i.e., r, R^2, regression, ANOVA, or t-test data). It was hypothesized that the implementation of PLCs in preK-12 schools would result in increases in student achievement in reading and math, and that collective or teacher efficacy, would serve as mediating variables between PLCs and student achievement. A final set of 21 dissertations was included in this analysis. Based on the Hord model, analyses for PLCs and student achievement in reading and math as well as separate analyses for each PLC component were conducted to determine if significant relationships existed between PLC implementation and student achievement. Results indicated that Shared and Supportive Leadership, Shared Vision, and relational factors of Supportive Conditions were influential in these analyses. Although the hypothesis that PLC implementation significantly increases math achievement was not supported, the hypothesis that PLC implementation significantly increases reading achievement was partially supported. The third hypothesis, collective or teacher efficacy, are mediating variables between PLCs and student achievement was also partially supported. Implications for practice and future research were included.