Mathematics teachers at the local middle school located in a southeastern suburban community were struggling to implement differentiated instruction (DI) strategies in mathematics lessons as presented in professional development (PD) sessions and as directed by school administrators. The purpose of this study was to explore middle school mathematics teacher perceptions about using DI strategies in the classroom, about the problems they may encounter trying to use new strategies presented in PD sessions, and about teacher ideas for improving PD sessions about DI. This research study was guided by Tomlinson's framework for differentiation in instruction. The research questions examined teachers' perceptions on implementing DI strategies learned in PD sessions, the challenges teachers face with implementing DI, and the ideas teachers have for improving PD sessions about DI. A basic qualitative design was used to capture the insights of eight purposefully selected mathematics teachers through semistructured interviews. Themes were identified through open coding. The trustworthiness of the study was established through member checking, rich and detailed descriptions, and researcher reflexivity. The findings revealed that teachers use student data to plan for DI, but that many teachers need and want more training to organize DI experiences. A professional development project was created to provide teachers with strategies and approaches for implementing DI to address individual learning needs of students. This study has implications for positive social change by providing a PD plan to help teachers overcome the challenges they face with implementing DI, and by creating a differentiated learning experience for all students. [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.]