Teachers need access to quality professional development (PD) to navigate the complexities of the teaching profession. An important aspect of this PD is that it is differentiated to meet the needs of teacher-learners with varying ability levels, teaching experiences, content knowledge, and teaching contexts. Stakeholders need access to high-quality research to attend to these diverse needs in PD. My dissertation consists of three connected Systematic Literature Review studies that examine the current quality of PD research at the secondary level, to determine what research says about differentiating for teacher-learners to provide guidance for education practitioners who make PD decisions. The first study is a systematic literature review to determine the current quality of PD research. Study II identified high-quality PD research and to what extent it supports differentiation practices. Study III is a review of three practitioner journals to determine to what extent the recommendations made in these journals are consistent with what the high-quality research supports. I concluded that while differentiation practices are beginning to make their way into PD research and conversations, more high-quality research is needed to identify effective ways PD can be tailored to meet the needs of individual teachers to ultimately improve student learning outcomes. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]