In this article, the authors describe how their first-grade class used the book "Inch by Inch" (Lionni 1960)--the story of an inchworm that escapes from a hungry robin by proving he is useful for measuring--as inspiration for a lesson focused on exploring length measurement through examining the meaning of an inch. The authors designed a task in which students investigated different paths a worm could travel to get from one side of a garden to the other. To build a greater understanding of the idea of a unit and how units might be used to measure different paths, the lesson requires students to work through and make sense of common misconceptions (i.e., leaving gaps between units or overlapping units). The authors wanted students to explore their own conceptions and ideas rather that just focusing on correct representations. To understand and make sense of students' thinking, they focused on posing questions that investigated what the students did and why. A bibliography is included.