This study explores how a problem-solving based professional learning community (PLC) affects the beliefs, knowledge, and instructional practices of two sixth-grade mathematics teachers. An interview and two observations were conducted prior to beginning the year-long PLC in order to gather information about the participants' beliefs, knowledge, and instructional practices. Five PLC meetings were held throughout the year focused on implementing problem-solving activities into the classroom as a means to create a mathematics learning environment more aligned with the "Standards" (NCTM, 2000). Three observations of each participant were made while they incorporated a problem-solving activity into their classroom. Finally, a post interview and observation were conducted at the end of the year to again gather information on the participants' beliefs, knowledge, and instructional practices. Results indicate that the year-long problem-solving based PLC was effective in moving the participants' beliefs, knowledge, and instructional practices towards a more reform-based vision of school mathematics. The similarities and differences between the changes that both participants went through as well as factors that may have influenced them are also discussed. [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.]