The purpose of the study was to investigate secondary students' understanding of the descriptive and predictive nature of teaching models used in representing compounds in introductory organic chemistry. Of interest were the relationships between teaching models, scientific models, and students' mental models and expressed models. The results from classroom observations, interviews with students, and completion of student questionnaires showed that the majority of students involved in this study had a sound understanding of the descriptive nature of teaching models but their understanding of the predictive nature of those models was limited, despite their experience in using a variety of representations in chemistry class. The data suggest that teaching models can play a pivotal role in initiating students' development of scientific models, mental models, and expressed models. In light of these results, it is suggested that teaching models be used to predict, test and evaluate conceptions similar to the way that scientists use scientific models so that students appreciate the similarities of teaching models and scientific models.