Traditionally, assessing student writing ability has often been product-focused. Advocates of child-centered process-oriented classrooms, however, suggest that teachers should also focus on understanding children's writing behaviors in the context of meaningful communicative tasks. In such an approach, writing conferences are one way in which teachers can gather information to use for teaching purposes. While engaging with children around writing, skilled teachers can make the most of writing conference interactions by taking advantage of the "teachable moments" that children present to them. In this article, we will discuss teachable moments as powerful instructional episodes in which assessment and teaching mesh to produce a finely tuned instructional system that moves students forward. We identify and explore three key hallmarks of the teachable moment as assessment and instruction in action, and discuss how teachers can make the most of these seemingly simple, but instructionally complex events. (Contains 2 figures.)