The mathematical behaviors of a group of seventh grade students were observed as part of a longitudinal study of how children build mathematical ideas. The children, having built representations of their solutions to a combinatorics task, were challenged by their teacher to explain and discuss their ideas, and to extend them to similar situations. This report focuses on how teacher questioning facilitated students as they: (1) justified their ideas; (2) extended ideas to problems with similar structure; (3) made connections to previous tasks; and (4) generalized their conjectures in the context of isomorphic problems. (Author/MKR)