This study investigated the ways in which a teacher developed conceptions of measurement teaching and learning as she collaborated with a researcher to learn and implement a measurement learning trajectory with two of her students. Teachers need tools that effectively address the content area of measurement and can be used to improve their understanding of students' thinking strategies in this area. One potential tool is a formalized Learning Trajectory (Clements & Sarama, 2004) and researchers have found that teachers' use of measurement learning trajectories facilitate all children's learning and especially those children who may have missed opportunities to develop higher levels of thinking strategies (Clements & Sarama, 2007). The intent of this study was to develop and employ a collaborative professional development approach involving extensive tutorial work with two students on measurement topics in Grade 5. In particular, the collaborative approach centered on the use of learning trajectories for length and area to guide instructional decisions in working with two students during one-on-one interviews. Similar to aspects of the Cognitively Guided Instruction professional development program (Fennema, Carpenter, Franke, Levi, Jacobs & Empson, 1996), the teacher reviewed literature related to students' understanding of measurement concepts, analyzed student work and interviews, developed tasks for future interviews with respect to the learning trajectories and completed weekly professional development tasks. Accounts of teacher knowledge and practice development (Heinz, Kinzel, Simon, & Tzur, 2000) were used to describe this process and highlight which aspects of the professional development experience supported the teacher's professional growth and which aspects had less impact on the teacher's growth. The results indicated that the teacher shifted from a Level 2 to a Level 4-A on the CGI framework for teacher knowledge developed by Fennema and her colleagues (1996). [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.]