The purpose of the present study was to analyze the behavior patterns of mentally retarded children in a special class and to discuss the application of results to the teaching method for them. A special class consisting of 15 male moronic children, who did not have gross neuro-motor symptoms, was used. We classified them into the three main types according to observations of their behavior-tendencies in daily life : A) the basic type without emotional disturbance, B) the excitable type charcterized by hyperactivities and, C) the inhibited type characterized by hypoactivities. We recorded particularly each response to each stimulus given by the teacher during lesson-hours. Each response could be analyzed according to its nature into either as a goal-directed response (+) or a non-directed response (-). A-type children presented significantly much more (+) responses than the other types of children. Frequency of (+) response by each child was related more closely to his type than to his intellectual level. Each stimulus by the teacher was sorted into either the one presented to all class members simultaneously (SA) or the one presented to each individual child by menas of designating him (SB). While A-type children could respond goal-directedly under (SA) situation, B-and C-type children still presented many (-) responses even under (SB) situation where their own names were designated. The most of the (-) responses by B-tpye children were to distub other membrs, but the ones by C-type children were autistic and dream. To lead B-type children into the learning process, more stimuli must be added which control to canalize their hyperactivities into the goal of learning. For C-type children, more stimuli which motivate them to learning must be added. A Sociometric test was given to this special class. The central part of the class was occupied by A-type children, C-type children were locatep on the peripheral zone, and B-type children were located on the intermediate zone. To apply these findings to the teaching method, the calss was divided in to the three groups. In each group, its members were made homogeneous in regard to their type and their intellectual achivement level. Each group has been taught by each one of three teachers. This method has become effective on increasing the (+) responses and improving the achivement level of the children involved.