This study was designed to determine whether or not the use of focused professional development using a checklist based on the Common Core State Standards Mathematical Practices impacted students' math scores as measured by an assessment that requires the use of the practices. Additionally, the researcher sought to determine whether or not the use of the focused professional development and a checklist impacted teachers' perceived level of understanding and level of comfort regarding the implementation of the Mathematical Practices in their instruction. The methodology used in this study was quantitative and the research design was quasi-experimental. Teachers in the treatment group completed two questionnaires, one administered at the start and at the end of the study. The results of the questionnaires were compared, embedding a small qualitative aspect into this study as the questionnaires contained open-ended questions, and questions relating to the participants' opinions. Additionally, teachers in the treatment group submitted a weekly checklist and a brief reflection detailing the impact of the professional development on their instruction. Testing revealed there was a significant difference between the groups at pre-test and a significant difference between the groups at post-test with the students in the non-treatment group outperforming the students in the treatment group. Questionnaire results provided evidence that the professional development corrected misperceptions that the teachers had and elevated their instruction. This professional development model may be adapted and used in other disciplines as schools examine ways in which they can provide targeted professional development regarding the transition to the Common Core State Standards. [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.]