The purpose of this applied research study with a program evaluation was to answer fundamental questions about the effectiveness of an extended professional development program. The program sought to promote quality mathematics instruction by increasing teachers' knowledge of and supporting the implementation of effective mathematics teaching practices in classroom instruction to address pandemic learning loss. To support the efforts of the Mississippi Department of Education to address pandemic learning loss and increase the capacity of the state's educator workforce, the professional development team in the Office of Professional Development created an action plan. A program evaluation was used to measure the effectiveness of this applied research study using a program evaluation design. Quantitative and qualitative methodological triangulation occurred by combining the data collection methods through a plan-do-check-act cycle of continuous improvement. Findings show a perceived increase in teachers' knowledge of effective mathematics teaching practices; however, implications for deepening understanding and securing external accountability were identified. The degree to which organizational improvement occurred will be measured by the collaboration across departments at the Mississippi Department of Education to help strengthen school improvement efforts with a focus on quality Tier 1 instruction. [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.]