The purpose of this quantitative study was to investigate the extent to which professional development practices in professional learning communities are consistent with research-based principles of effective professional development. Additionally, the study investigated potential differences in the content focus, active learning, coherence, and duration features of professional development practices in professional learning communities between elementary, middle, and high school teachers. Data on professional development practices were collected from 128 teachers from four elementary schools, three middle schools, and two high schools using a survey instrument. Analysis of the data using descriptive statistics and a mixed model ANOVA suggested that there was a highly significant difference in the factors (Factors) of effective professional development within professional learning communities across all grade levels. However, for the main effect of grade levels (Levels), there were no overall significant differences in elementary, middle, and high school teachers. The ANOVA results for the main effect of Factors X Levels indicated that the mean scores for the five factors were significantly different across grade levels. Further data analysis, a one-way ANOVA and a LSD test, revealed statistically significant differences in the means of the Active, Content, and Duration factors of professional development within a professional learning community across grade levels. The data also suggested there was no statistically significant difference in the Coherence factor of effective professional development across elementary, middle and high school teachers. [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.]