Children are guided by constraints and biases in word learning. In the case of the shape biasthe tendency to extend count nouns by similarity in shapeprevious findings have revealed that learning plays an important role in its development (e.g., Smith et al., 2002). Some have proposed that children acquire inductive constraints like the shape bias by making inferences about observed data on multiple levels of abstraction (e.g., Smith et al. 2002; Kemp et al., 2007). The current study provides support for this hypothesis by demonstrating that preschoolers can rapidly and flexibly form overhypotheses about the role of arbitrary features, not just shape, in determining how words refer to object categories. This work suggests that when learning individual words, children are also learning about words simultaneously. Childrens ability to learn to learn may have implications for the origins of learning biases in many different cognitive domains, not just in language learning.