The purpose of this phenomenological research study was to use Self-Determination Theory as a framework to analyze middle school mathematics teachers' motivation to attain effective professional development concerning Ohio's Learning Standards as well as other instructional aspects that affect the classroom. Teachers are exceptionally busy meeting the daily demands that exist in the realm of education. They often take it upon themselves to further their education by pursuing graduate degrees and participating in required professional development involving all aspects of education. Furthermore, the Ohio school systems have adopted the Common Core Standards as well as the American Institute for Research's Ohio Computer-Based Assessments which has compelled mathematics teachers to not only change the order in which they instruct the mathematics standards, but how they instruct. This study will utilize the Self-Determination Theory (Ryan & Deci, 2000) as a framework to research the motivation behind teachers' will to pursue professional development to satisfy internal needs of self-improvement involving instructional methods in order to ensure success in the classroom involving both instruction and assessment. The results of the findings of the study indicated the three basic psychological needs of autonomy, competency and relatedness must be met to foster intrinsic motivation. Those teachers that were intrinsically motivated were more likely to engage in effective professional development and often exceed expectations conveyed by their school districts. Effective professional development incorporates a learning environment that acknowledges the research regarding adult learning contexts, including aspects of situated learning. [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.]