Students often view their role as that of a replicator, rather than a creator, of mathematical arguments. We aimed to engage our students more fully in the creation process, helping them to see themselves as legitimate proof creators. In this paper, we describe an instructional activity (i.e., the "group proof activity") that is purposefully designed to support students' development as creative provers. We demonstrate how one group's attempt at constructing a group proof allowed the group members to build on one another's individual ideas to improve their strategies for proving and to address important misconceptions in their original work. The case highlights how the group proof activity supports a classroom environment where student ideas drive the discussion while also allowing for important mathematical ideas related to proof to become the central focus of a group's learning.