A category system was developed to describe content development in chemistry classes. The instrument had three broad dimensions: the Semantic dimension for coding the intent of the teacher in developing content; the Syntactic dimension for coding the actual meaning of the communication; and the Initiate-Supply dimension for coding the participants in the communication. Subcategories were developed, and a series of teaching strategies describing content development using the categories were proposed. The instrument was used to investigate the development of chemistry content by seven CHEM Study teachers. Each teacher was audiotaped during nine class periods, and "content events" were transcribed to cards and classified. Data were analyzed both as percentages of events in each subcategory and as transition matrices. The extent of participation of teachers and students in each kind of event is reported, and common patterns of content development are identified. The results of the study suggests that the teachers in the sample adopted a deductive teacher-oriented approach to teaching content. (EB)