The present research involves an interpretive examination of the way in which two experienced teachers of science use their subject matter knowledge in the classroom, the planning or preactive strategies used for classroom presentations, the nature of the examples used to illustrate aspects of subject matter during the interactive phase of teaching, and the reaction of students to these issues. Utilising an interpretive methodology, the classroom practice of the two teachers was observed and these teachers were then interviewed about various aspects of planning and presentation. The students who were present in both classes were also interviewed in order to expand the source of data for the study. The findings of this research are presented at six assertions which address specific aspects of the research questions. In the preactive or planning phases it is asserted that experienced teachers of science reject formal or structured planning in favour of a more globally oriented planning strategy. This strategy is informed by previous episodes and experiences both within and outside of the classroom. Further claims are made about the subject matter knowledge, representational repertoires and reinforcement strategies of experienced science teachers during the interactive teaching phase. These claims strengthen the overall proposal that these teachers utilise a detailed and diverse comprehension of their subject through a favoured teaching style or repertoire. Evidence for the use of alternative repertoires, and particular example schema is presented. It is also asserted that senior science students have particular preferences for the repertoires and strategies used in class, but may experience cognitive discomfort when they are unable to negotiate the academic demands of the classroom.