This study investigated professional development practices and its impact on classroom instruction as perceived by teachers in participating school districts in Mississippi. One hundred and twenty-one teachers who participated in this study responded to Learning Forward's Standards Assessment Inventory (SAI) using the Survey Monkey platform. This survey included demographic questions that gathered information about the characteristics of the respondents. These questions focused on key factors that concentrated on essential elements that enable a more thorough examination of data. The survey also included questions from the following key areas that pertain to educator learning: Rigorous Content for Each Learner, Transformational Processes, and Conditions for Success. This quantitative study aimed to determine teachers' perceptions of professional development and its influence on instructional practices in the 21st-century classroom. An analysis of the hypotheses was conducted using a sample t-test and ANOVA. The findings indicate there were no statistical differences between teachers' perceptions of professional development practices and teachers' years of experience, assigned role, years at current school, or gender. However, there was a statistically significant difference between elementary and high school teachers' perceptions of professional development and curriculum implementation. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]