Items from a widely used standardized reading achievement test were rated by trained judges according to the degree to which they required an understanding of hierarchical classification. Two subtests were constructed from subsets of items that were identified by their extreme ratings. Subtest A was judged to require classification operations from respondents; subtest B was judged not to require them. Twenty-two third grade students were assessed on five Piagetian classification tasks and designated as classifiers, transitional, or nonclassifiers on the basis of this assessment. The subjects were then administered subtest A and subtest B. Analysis of covariance of the subtest A scores (effects of subtest B controlled) revealed a significant effect for group placement. The results were interpreted to mean that reading test performance is partially influenced by the student's mastery of hierarchical classification because some test items require this ability. Such items discriminate among children on the basis of developmental maturity rather than on instruction-related knowledge. (Author)