This mixed methodology study investigated the affects teacher training, or professional development, have had on the implementation of differentiated instruction in elementary classrooms. The study was conducted in a Southeastern Georgia school district. Data was collected using surveys and interviews. The surveys contained 20 questions and asked teachers to answer each question using a Likert Scale, which provided the researcher with quantitative data. There were 75 teachers surveyed. The interviews consisted of 15 open-ended questions and were conducted face-to-face with 10 teachers from the district studied, and provided qualitative data. The data showed that overall, teachers in the district had a positive attitude toward differentiated instruction, and its implementation, and were comfortable implementing differentiated instruction in their classrooms. Results of the data also revealed that the majority of elementary teachers who participated in the study reported that they had attended some type of professional development provided by the school district. Overall, teachers in the school district had a clear understanding of what differentiated instruction felt that it was necessary for student success in their classrooms. [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.]