The purposes of this study are, first, to clarify the teachers' teaching patterns and pupils' behaviors in the classes for the mentally retarded, and secondly, to evaluate the effects of such patterns of teaching, not at the ideational level, but at the more concreate and practical level. Two classes for the mentally retarded in two secondary schools, which had already been verified in our previous research as having different typical patterns, were chosen as our samples for the following case study. In the present study, we atteinpted to observe and evaluate the classes under two kinds of conditions. One is to clarify the teaching pattern shown by each teacher and the pupils' behavior in the regular class-room situation, and the other is to analyze the pupils' behavior changes in the experimentally constructed situations where the temporary leaders, taking the place of the regular staffs, are to take their roles as either directive or non-directive type of leadership. As our procedure, such a teaching situation was filmed and recorded at the first step. Then some raters were instructed to rate the teacher-pupil interaction, teacher's personality, class-room atmosphere and pupils' behavior using seven point scales.