The purpose of the study was to examine how action research informs instructional changes that need to take place in the middle grades mathematics classroom. There is a need for an increase in engagement in middle grades mathematics by educators being critically reflective of their instructional practices. The research question addressed in this study: How do I systematically reflect upon and change my mathematic instructional design through the process of action research? The qualitative methodology for this study was implemented through the process of action research. The researcher used daily journal reflections, student conversations, weekly lesson plan feedback, and achievement data to inform instructional changes grounded in constructivism within each round of data collection. Qualitative data analysis indicated that the action research process promotes reflection that shows critical instructional changes that may be hidden behind a teacher's daily routine of instruction. Data also present the need for challenging work for high achieving students to promote engagement, confidence, independence, and persistence. Action research is critical to educators' instructional practices because instructional design should morph to meet the needs of learners. Recommendations for future research include increasing low-ability student engagement, creating mindful engagement conversations with low-ability students, and implementing engagement strategies to promote grade-level content understanding for low-ability students. The researcher hoped to provide insight on the importance of incorporating action research into daily instructional practices to meet the needs of all learners. [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.]