Three theoretical frameworks were used to guide this intervention case study: dividing fractions; sociomathematical norms, and justification. Middle school mathematics students were given the opportunity to solve partitive and measurement division of fraction word problems with different contexts. The teacher purposefully implemented a sociomathematical norm that an explanation consists of a mathematical argument, not simply a procedural description or summary. In order for students to justify based on reasoning they were expected to use three guiding principles: convince themselves by making personally-meaningful solutions to problems; convince others by communicating their understanding through graphic representations, words (written and oral), and symbols; and make sense of other students' justifications to raise challenges if disagreements occurred. The case of one student was documented in depth. Three claims emerged from the three guiding principles: Taylor was aware of her own thinking and learning so she used strategies that made sense to her; Taylor was not always explicit about the unit as a whole, and she was not always able to convince others; and Taylor asked clarifying questions when she disagreed with another student's justification. [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.]