The purpose of the present study was to examine the perception of one's own and others' ability, and to find developmental changes in the affect aroused by the perception in childhood. Elementary school children (1st, 2nd, 3rd, 5th and 6th graders, N = 237) completed a questionnaire. In the questionnaire, children were asked to assess the ability of self and a close friend (a psychologically close other) and guess their affect when making comparisons of their own ability with that of a close friend and an imaginary new student (a psychologically distant other) in their most and least favorite subjects. The major findings were as follows: (a) First and 2nd graders perceived their own and a close friend's abilities in a similar way to 3rd graders and above (e. g., Isozaki, 1994). However, the dynamic processes of the ability perception in 1st graders seemed to be different from those in 2nd-3rd graders and 5th-6th graders. (b) There were developmental changes in the affect aroused by the comparisons of the ability. The ability perception and the affective arousal by such perceptions changed about between the 2nd and 3rd grade (around the age of 8 to 9 years).