The purpose of this study was to create a model of Differentiated Professional Development (DPD) that is a more effective method of professional development due to the addition of the principles of differentiated instruction (DI). The DPD model was created by combining previous studies on effective elements of professional development with the theories of DI and organizing them into a flexible model for all settings to use. A qualitative grounded theory approach utilizing a focus group and semi-structured interview format was used to collect data from the 21 participants representing secondary teachers and administrators. Through the use of both open and a "priori" coding 18 themes emerged from the focus groups reflecting their opinions and PD as well as the viability of the DPD model. The findings from the analysis indicate a strong support for the addition of DI to PD as well as the overall DPD model. [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.]