The purpose of this study was to examine the effect that large within-examinee item difficulty variability had on estimates of the proportion of consistent classification of examinees into mastery categories over two test administrations. The classification consistency estimate was based on a single test administration from an estimation procedure suggested by Subkoviak (1976). The Fundamentals of Nursing, an ACT Proficiency Examination Program test, was administered. This test consists of item sets from six subject matter categories ranging in length from 8 items to 52 items, with the average length approximately 20 items. Analyses of both actual and simulated data revealed that the use of a single, overall-item difficulty estimate for an examinee's true-score, even when item difficulty varied greatly within an examinee, did not influence the estimation of the proportion of consistent classifications any more than homogeneous difficulty situations. (Author/PN)