Underrepresentation of people of color in mathematics at the postsecondary level warrants more focus on equity issues. The prevalence of cognitive studies at the undergraduate level is met with the call for critical analysis about the kinds of knowledge that get privileged in mathematics education. Connecting to the Funds of Knowledge work, this paper discusses the utility of diSessa's Knowledge in Pieces cognitive framework to uncover productive informal knowledge in learning formal mathematics. Seeing the valorization of knowledge as related to issues of power, a case of a Chicana student's productive sense making about the formal definition of a limit illustrates the way diSessa's framework can help challenge what counts as productive mathematical knowledge and reasoning. [For the complete proceedings, see ED583989.]