Linear functions are an important part of the middle school mathematics curriculum. Students in the middle grades gain fluency by working with linear functions in a variety of representations (NCTM 2001). Presented in this article is an activity that was used with five eighth-grade classes at three different schools. The activity contains 15 cards that can be sorted to create 4 sets of cards, with each set representing one particular linear function. Some cards will not fit into any set, which automatically increases the cognitive demand of the task.