For decades, teacher educators have struggled to better prepare teachers who critically understand and utilize second language acquisition (SLA) theory and research. Using a sociocultural theoretical framework that positions teacher-learners as active users and producers of SLA theory, this study explores how teacher-learners in two sections of one capstone SLA course (offered in a graduate-level TESOL/World Language teacher education program) construct their SLA knowledge and praxis. We used thematic content analysis to examine our data set which included written artifacts teacher-learners produced during their course assignments, online discussion posts, observations of class discussions over sixteen weeks, and three questionnaires (completed before, in the middle, and at the end of the course). Findings revealed how teacher-learners externalized their understanding of SLA, struggled with contrasting perspectives, and resituated theory in light of past, present and future teaching. This study has implications for L2 teacher education by shedding light on processes of teacher learning and by offering an inquiry based model for SLA courses that prepare teacher-learners as transformative intellectuals and lifelong learners. (C) 2016 Elsevier Ltd. All rights reserved.