This study documents the kinds of planning that teachers engage in before a lesson begins and identifies differences in planning procedures between teachers. The subjects were 40 second- and fifth-grade teachers in California including 20 teachers with high average pupil gain scores and 20 teachers with low average pupil gain scores. The teachers were provided with special curriculum materials for one lesson in reading and one in mathematics and were asked to adapt these materials for use in their own classoooms. Each teacher planned and conducted a 20-minute lesson in each subject area. Patterns of similarities and differences in response to the lesson planning task were identified. Teachers varied in specificity, format, and types of information included in written plans, used behavioral goals rarely, made more specific than general statements, and referred frequently to cognitive aspects of the lesson. No teachers mentioned seating arrangements, though it was obvious from observation of their lessons that seating arrangements were a planned aspect of most lessons. Comparative data on seating arrangements indicates some significant differences between teachers with high and low pupil gain scores--teachers with low pupil gain scores showed a tendency to be inattentive to the appropriateness or comfort of physical arrangements of their pupils. Teachers with high pupil gain scores showed a greater attention to cognitive aspects of lessons and were the only ones to develop original behavioral objectives; teachers with low pupil gain scores tended to think in generalities rather than specifics. (MM)