An increasing number of researchers have contended that the process of teaching is composed of thoughts as well as actions and that a complete understanding of teaching cannot be achieved if research is limited to observable teacher performance alone. A study was designed to examine: (1) the nature of teacher thoughts before and during lessons; (2) the relationship between teacher thoughts and actions; (3) the reasons teachers offer for their thoughts; and (4) the circumstances they believed accounted for teaching success. Data was gathered from three experienced teachers and three student teachers. They were asked to capture their pre-lesson planning thoughts by writing their thoughts as they occurred during the planning process. A stimulated-recall procedure was used to help them identify incidents in the course of the lessons where their thoughts and feelings had been clearly and consciously registered. They answered a questionnaire immediately after they completed their pre-lesson planning and participated in a structured interview. Common to all of the teachers was the view that lesson plans were necessary for their "security." This sense of security rested on the knowledge that at any point in the lesson they knew what they might or should do next. They also felt that when they planned in advance, they were likely to find more opportunities to consciously and calmly contemplate a lesson, its problems, and possible solutions to those problems. Often, however, circumstances made it necessary for the teachers to change or modify their plans. As a result of the teachers' responses, a conclusion is that teacher education programs should emphasize diversity rather than uniformity in lesson plan instruction. Samples of the teachers' planning sheets and responses to interview questions are appended as well as a bibliography of 37 studies on teacher thought processes. (JD)