This paper focuses on an analysis of relationships among interactive behavior, interactive decision making, and interactive processing of information about pupils as perceived by teachers in the course of a lesson. Three teachers participated in the study. In response to a general request to state their plans for the lesson, the teachers consistently mentioned content to be covered and activities to be engaged in, and frequently mentioned the materials to be used in the planned lesson. The influence of the discrepancy between the teacher's expectations and the actual events during the lesson on teacher decision making is illustrated in three case studies corresponding to three different degrees of teacher-perceived discrepancy between plans and classroom reality. (JD)