Reform efforts in science education have focused on engaging students in authentic scientific practices. For these efforts to succeed, detailed articulations of scientific practice need to be linked to understandings of classroom practice. Here we characterize engagement in practice generally in terms of "3Rs": routines, roles, and responsibilities. We argue that there is a misalignment between the 3Rs of scientific practice and the practices common in classrooms, and that this misalignment poses a considerable obstacle for beginning teachers who attempt to implement reform pedagogy. As part of a secondary methods course, 16 preservice teachers (PSTs) participated in two exemplar activities designed to engage them in scientific practices. The PST performances suggest that at least initially, they did not consider authentic scientific practices appropriate for classroom activities, implying a pedagogical repertoire dominated by the 3Rs of traditional classrooms. PST performances, however, evidenced a shift in the 3Rs from those common in classrooms to those required by these activities, suggesting that their visions for classrooms are malleable and underlining the importance of aligning the 3Rs of scientific and classroom practices during teacher preparation.