This study was designed to discover the nature of interactions between effective teachers in regular-sized 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 teacher 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-sized classes. The a prior categories of R. French and C. Galloway (1970) of institutional tasks, personal, and mixed were used to determine if the data gathered were consistent with interactions previously recorded (C. Evertson and J. Folger, 1989). As in previous studies, teachers in the small classes spent more time on task-related interactions than teachers in the regular-sized classes. Teacher in regular classes spent more time on institutional interactions. The emergent categories of positive attention and examples, negative attention, acknowledgment, directives, and procedural were documented. When all of the interactions were compared, teachers in small classes were observed sharing more separate interaction events than teachers in regular-sized classes, and they were devoting more time to interactions that were task-related and less time to negative behaviors than the regular-sized classroom teachers. Those teachers spent more time on interactions that were not related to the learning objectives. Administrators must consider the impact of primary classes with fewer students. Interactions are one facet of this complex environment. Students and teachers benefit from reflective practice involving productive, nurturing interactions. (Contains 2 figures, 1 table, and 45 references.) (Author/SLD)