This paper explores how two teachers concurrently enacting the same technology-based inquiry unit on evolution structured activity and discourse in their classrooms to connect students' computer-based investigations to formal domain theories. Our analyses show that the teachers' interactions with their students during inquiry were quite similar, and each teacher used whole-class discussions as a major vehicle for connecting students' understanding to formal domain theories. Each teacher, however, structured the discourse in these discussions quite differently. We interpret these differences as each teacher navigating a set of trade-offs to balance, on the one hand, opportunities for students to actively develop their own ideas, and on the other, their concerns that students develop normative understandings. We identify several dimensions of trade-offs that emerge from our data, and suggest how teachers' choices on these dimensions shape students' opportunities for learning.