The purpose of this study was to compare the classroom climates of junior high school students in relation to sex and achievement. A Chinese version of Barclay Classroom Climate Inventory (BCCI) was administered to 450 children, 228 boys and 222 girls, sampled from two junior high schools. It was found that: (1) Pupils with higher achievement showed higher scores in self-competency, achievement-motivation, and vocational interests. They also earned more teacher approval than pupils with lower achievement. There were no significant differences in peer nomination scales between different achievememt levels. Low-achieving children expressed more tendency to associate with the peers than high-achieving children, They appeared to have a higher level of social interacton in the classroom. (2) Boys and girls differed significantly on most BCCI scales. Boys not only expressed more self-competency, energy and positive attitude toward school, bat also earned more positive and negative teacher ratings than girls. According to the BCCI vocational scales, boys showed more interests in outdoor and physical activities as well as intellectual-scientific work. Girls, on the other hand, showed more social, conventional, artistic and controlled approach than boys. Boys received higher scores in school-orientation with particular suspectability to teacher´s praise, while girls expressed family-orientation wills a liking for sharing activities with their parents. In addition, boys indicated a stronger drive for leadership and success is relating to other people than did girls.