Factors influencing teachers' decision making in the classroom were studied. Fourteen elementary school teachers in five schools were observed and interviewed. Observations focused on formal, organized classroom activities, and interviews centered on what basis, or for what reason, a particular procedure or curriculum material was employed. Types of support components available to the teacher in making decisions included colleagues, mandated district curriculum, published research, textbooks, commercial publications, the school principal, and personal experience. The teachers ranked student characteristics first and curriculum materials second as factors influencing how they proceed in the classroom. An inservice training program, referred to as Professional Development Program Improvement Center (PDPIC), was cited as a valuable source of decision making support, as well as the "Stull Objectives," a teacher improvement system similar to PDPIC but focusing on behavioral management. Colleagues were also seen as supportive, in particular when acting as part of a team. A microcomputer was cited by one teacher as a source of support. Extensive observational and interview data is presented on 3 of the teachers, and data from the other 11 are summarized. The questionnaire used in the study is appended. (JD)