Collaborative engineering design projects are fraught with subjective uncertainty associated with task issues ranging from understanding math and science concepts, to manipulating technological and digital tools and evaluating design ideas. Also, engineering design projects are contexts in which uncertainty is likely to stem from social issues as students encounter unfamiliar sociocultural practices and as individuals with diverse histories, beliefs, motivations, expectations, and values attempt to share the small space of a classroom. This qualitative discourse analytic study relies on observations and interviews to examine how social and task uncertainty management varied across three groups of students engaged in a collaborative design project. Specifically we asked, (1) how do groups vary in their management of uncertainty during engineering design projects; and (2) how does variation in uncertainty management influence groups' design practices and products? Data were drawn from a larger project that took place over one-school year in an ethnically and academically diverse public fifth grade class in the U.S.