This collective case study used methods of discourse analysis to consider what computer-mediated collaboration might reveal about preservice teachers' sense-making in a field-based practicum as they learn to teach reading to children identified as struggling readers. Researchers agree that field-based experiences coupled with time for reflection benefit preservice teachers as they learn to teach reading. However, research is not as clear about which features of practicum experiences lead to preservice teacher learning, which may contribute to preservice teacher misconceptions, and how learning about reading instruction might be rendered more visible to researchers. Grounded in sociocultural perspectives, analysis focused on language as a mediating tool for the construction of knowledge. Data collection spanned three semesters in a literacy assessment and intervention practicum. Preservice teachers constructed understandings of readers and reading instruction through reflecting, planning, and articulating their decision-making processes with one another in the online discussion board. Findings indicated that analysis of preservice teachers' computer-mediated discussions provided a window into their sense-making processes. While some preservice teachers' discourse demonstrated marked growth, other preservice teachers' limited use of precise language related to reading assessment and intervention frequently inhibited their developing understandings and instructional decisions. As well, some of the decisions instructors made likely contributed to several PST misconceptions. We conclude with implications for computer-supported collaborative environments in teacher education as a means to make preservice teacher learning more visible and accessible as a tool for teaching and learning.