This article suggests that productive disciplinary engagement can be fostered by designing learning environments that support (a) problematizing subject matter, (b) giving students authority to address such problems, (c) holding students accountable to others and to shared disciplinary norms, and (d) providing students with relevant resources. To provide empirical support for this suggestion, we use these 4 guiding principles to explain a case of productive disciplinary engagement from a Fostering Communities of Learners classroom. We use the principles to understand 1 group of students' emergent and sustained controversy over a species' classification. The students became passionately engaged, used evidence in scholarly ways, developed several arguments, and generated questions regarding biological classification. We propose the controversy as an example of productive disciplinary engagement, and show how it was supported by: the treatment of the classification as a legitimate problem by the students and teacher; the students having the authority to resolve the issue for themselves while being held accountable to relevant contributions from peers and outside sources as well as to classroom disciplinary norms for using evidence; and students having access to multiple sources of information, models of argumentation, and other relevant resources. The article closes by reflecting on the generality of the principles, showing how they can be used to understand 2 other cases of productive disciplinary engagement from the literature on reform programs in science and mathematics. By specifying differences as well as similarities in the ways the principles were embodied in these cases, the article may provide learning designers with a landscape of possibilities for promoting the specific kinds of productive disciplinary engagement that they most value.