This study, using the Self-Observation Scales (SOS) primary and intermediate levels, was conducted to determine whether the self-concept items that were most predictive of reading achievement varied among sex-race-grade subsamples and to examine specific item content in order to focus upon the nature of the relationship between reading achievement and self-concept. It was hypothesized that the set of items most predictive of reading achievement for a particular sex-race-grade subsample is constant across all sex-race-grade subsamples on the Primary Level of the SOS, and the set of items most predictive of reading achievement for a particular sex-race-grade subsample is constant across all sex-race-grade subsamples on the Intermediate Level of the SOS. Subjects for this study were 5,990 children whose reading achievement data were recorded by their teachers during the process of validating and establishing norms for the SOS. Both hypotheses were rejected. (Author/RB)