All learning environments are characterized by numerous communication and interaction practices, which lend themselves to an overall characterization of the climate as defensive or supportive. A case study of public communication and interaction in a large, research-intensive university's first year computer science courses illustrates a learning environment primarily characterized by elements and behaviors associated with a defensive communication climate. Descriptions of classroom interactions and behaviors illustrate what a defensive communication climate “looks like” in terms of behavior, based on extensive observational research. Interview data demonstrates that defensive communication practices can lead to attrition among women in the major and illustrates ways in which the communication climate that characterizes the major is experienced and interpreted by women in the courses. This data also links defensive communication behaviors with lower confidence among women toward their major --- results consistent with previous studies of the causes of attrition among women in other Science, Technology, Engineering, and Mathematics (STEM) disciplines. Classroom experiences and behaviors that reflect a more supportive communication climate will be discussed within the context of practices and interactions that professors can engage in to ensure that their courses lean toward a supportive rather than a defensive environment as a way of making computer science learning environments more inclusive.