Mathematics curricula tend to focus either on the development of procedural knowledge or conceptual knowledge yet research support an iterative development of these knowledge types. Research also suggests that teachers should move beyond strictly using curriculum and move toward being the developers of their curricula. Using multiple case study analysis, this qualitative study explored the factors that influenced four middle school mathematics teachers as they planned and implemented mathematics tasks for their students. The participants were influenced by a variety of factors including time constraints, experience with teaching resources, connections with their students, and ability to be organized yet flexible with their planning and teaching. This study further investigated whether balancing the development of procedural and conceptual knowledge with their students influenced the teachers during the planning and implementation of mathematics instruction. The participants fell into two distinct groups. One group gave equal time to the development of the two knowledge types, but treated them separately, failing to assist their students with connections between concepts and procedures. The second group planned and implemented lessons that evolved from concrete to abstract while making connections between concepts and procedures. Neither group recognized the need for curriculum resources that could assist them with the task of connecting mathematical concepts to procedural skills. The field of mathematics education could benefit from additional research studies that engage teachers in the planning and implementation of units of study that both balance and connect conceptual and procedural knowledge with students. [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.]