Two teachers participating in an online study group provided the foci for in-depth case studies. Transcripts of conversations they had with colleagues about issues related to reform-oriented pedagogy were analyzed from both acquisition and participation perspectives on learning. Both teachers exhibited mainly marginal changes to their pedagogical reasoning structures and were generally resistant to adopting ideas posed during online debates. At the same time, the text-based environment provided a setting for both participants to structure their emerging thoughts about changes to their existing pedagogical reasoning structures. It also served as a forum for them to identify gaps in their personal knowledge and to obtain further professional development to address them. The methodology and theoretical perspective employed in the report provide a foundation for further research on teachers' learning in online environments.