The development of a category scheme for the systematic analysis of science classroom discourse is described. Three teaching models are discussed: the Impression Model, which depicts the mind of a student as receiving and storing external impressions; the Insight Model, which denies the possibility that ideas or knowledge can be conveyed by language, and describes knowledge to be the result of insight into meaning; and the Rule Model, which describes the intent of teaching to be the acquisition of knowledge. The characteristic features of these models constitute the analytical scheme which is used to identify the teaching models in transcribed chemistry and physics lessons in grades 11, 12, and 13. (MH)