For 2 weeks in the summer of 2018, K-12 STEM teachers (n = 40) attended a professional development (PD) that included four sessions focused on computer science modeling with follow-up academic year sessions; however, overall, the teachers did not meet expectations about what modeling means or how to utilize it. To examine why, the authors looked at the teachers' discourse. Using three theories to connect to the practice (terministic screens, schema theory, and concepts of capital) the authors analyzed the surveys, interviews, and email reflections to explore participants' concept of models and the potential difficulties of implementing computer modeling in their classrooms. Five general concepts of models are presented. Findings show that the term model was interpreted differently by the PD's faculty team and participants. Further, the authors found that the majority of presenters held differing theories of models than the participants. Participant concepts of models did improve slightly. Implications are provided showcasing articulated keys for delivering PD that assists in eliminating discursive and theoretical issues. Included are considerations for STEM teacher educators, PD providers, and K-12 teachers.