The construct validity of children's responses to the Self Description Questionnaire, the Perceived Competence Scale for Children, and the Multidimensional Measure of Children's Perceptions of Control was assessed. The tests' authors emphasized the importance of distinguishing self-perceptions in the physical, social, academic, and general content domains. Tests of this content specificity included factor analyses, multitrait-multimethod (MTMM) analyses, and patterns of correlations with additional criterion variables. The subjects were 510 7th, 8th, and 9th graders (42% female) from two single-sex private high schools in Sydney, Australia. The subjects' motivation and mathematics and reading achievement were also studied. Contrary to previous research, MTMM analyses of responses to the two self-concept instruments demonstrated their convergent and discriminant validity, apparently reflecting the improved design of these newer instruments. These findings and factor analyses of responses to the self-concept instruments support claims by S. Harter (1982) and by H. W. Marsh. For the perceived control instrument, however, there was little support for the discriminant validity of responses with respect to content domains other than the physical domain, calling into question claims by J. P. Connell (1985). Seven tables summarize data. (Author/SLD)