This study used a classroom interaction system to code three 20-minute episodes in each of 40 elementary classrooms. The procedure was followed in October and again in May. An analysis was made to investigate the relationships between aspects of teacher praise and student participation in classroom discussions. Findings indicated that (a) praise has a differential effect across children, (b) specific praise has a greater positive effect than stereotyped praise, (c) the effect of praise drops as the year progresses, and (d) the effect of mild criticism increases as the year progresses. (PB)