Organizational characteristics of two universities and two public school systems, as these characteristics related to student teaching, were compared at two levels: (1) the formal, documented guidelines, or "what's supposed to happen"; and (2) the informal, working practices, or "what's really going on" in the settings. This paper reports on findings concerning the classroom level. The first section discusses major findings about formal university organizational characteristics which had a logical impact on student teaching. The second section examines more informal university characteristics which influenced student teaching. In the third section, major findings related to formal public school characteristics are discussed, and the fourth section reports on major findings related to informal school practices. Findings resulting from a review of observational data are presented in the fifth section and are categorized into four general groups according to whether behaviors of cooperating teachers and student teachers involved interaction, and if they paralleled, converged, or diverged over the course of the semester. An analysis of the student teaching experience in different contexts points out the critical importance of the cooperating teacher. (JD)