As recommended by National Council of Teachers of Mathematics (NCTM), the first author regularly relies on her first graders' writing to assess their reasoning about important math concepts. Their writing serves as a culminating activity that allows her to better assess the depth of each student's understanding following class activities and discussions. She uses a talk frame to keep an organized record of a class discussion on the board and to explicitly connect what students have experienced and discussed as a class with their individual writing. This process allows her to first generally assess students and then progress to a more individualized assessment of their understanding. In this article, the first author analyses her teaching to determine what part of her instruction students drew from to express their understanding of symmetry in their writing. Although they used the notes on the talk frame as a reference for their writing, they also drew from the class activities and discussions. Her first graders generated new ideas and expanded on the thoughts that they had come up with as a class and had recorded on the talk frame. Using the talk frame to connect class activities and discussions with individual student writing showcases student ideas but does not hamper individuals from expressing their personal understanding. (Contains 8 figures.)