This report describes a study designed to discover the nature of teacher-student interactions in regular-size classes with 25 or more students and small-size classes with fewer than 18 students. Eleven public-school primary classrooms were observed, and the interactions between the teachers and students were studied. Verbal and nonverbal interactions were recorded and categorized using emergent and "a priori" categories to discover similarities and inconsistencies when comparing regular and small-size classes. Teachers in the small-size classes spent more time on task-related interactions than did teachers in regular-size classes. Teachers in regular-size classes spent more time on institutional interactions. The emergent categories of positive attention and examples, negative attention, acknowledgment, directive, and procedural were documented. When all interactions were compared, teachers in small classes were observed during more separate directive interaction events than were teachers in regular-size classes, and they were devoting more time to interactions that were task-related and less time to negative behaviors than were the regular-size classroom teachers. The regular-size class teachers spent more time on interactions not related to learning objectives. Students and teachers benefit from reflective practice involving productive, nurturing interactions and thus may, in part, explain higher achievement in small classes. (Author)