The purposes of this study were three-hold: (1) to compare and analyze the views of special class placement by special class teachers of 21 junior high schools in Taipei city, (2) to investigate the effects among the variables of sex, age, teaching experience, and professional training background of special class teachers in rating the achievement of MR students, (3) to compare the academic achievement and social adaptive behavior of two groups of MR students in special classes and in regular classes. The study consisted of two parts, a survey study was carried out in Study 1, in which the academic achievement and personal adjustment of MR students were measured by 176 special class teachers using rating scales. A pretest-posttest control group design was used in Study 2 to compare the efficacy of special class placement. The experimental group consisted of 30 students who had been placed in MR class for the first time during the 1981-82 school year. The 30 control students were eligible for MR placement, but were retained in regular classes during the entire school year. The sample was selected from 3 schools with MR classes and 3 schools without such classes. The result of this study revealed: (1) there were significant differences found among the special class teachers regarding attitude toward special class placement, (2) among the teacher´s groups in terms of age, sex, and teaching experience, no significant differences were found on the rating of the efficacy of special class programs, (3) over the six-month period, the special class MR students had significantly greater gains in arithmetic, but on no reading or social adaptive behavior.