Negative item bias is produced by the inability of preadolescent children to respond appropriately to negatively worded items on rating scales, and is hypothesized to be a cognitive-developmental phenomenon. The effect is examined with responses to the Self Description-Questionnaire (SDQ), a multifactor self-concept instrument. In study 1, response to positive and negative items were uncorrelated in grade 2 but were substantially correlated by grade 5. In study 2, confirmatory factor analysis of response by grade 5 students demonstrated that the negative items contributed both to the scale they were designed to measure and to a "negative item" factor. The negative item factor was nearly uncorrelated with any of the self-concept factors, but was substantially correlated with reading achievement. The two studies demonstrate that younger children and children with poorer reading skills are less able to respond appropriately to negatively-worded items, and that this effect produces a bias in their response to the SDQ. This supports the contention that the effect is a cognitive-developmental phenomenon. (Author/PN)