Standard unidimensional Rasch models assume that persons with the same ability parameters are comparable. That is, the same interpretation applies to persons with identical ability estimates as egards the underlying mental processes triggered by the test. However, research in cognitive psychology shows that persons at the same trait level may employ different strategies to arrive at the solutions. This is a major threat to the construct validity of a test since the construct representation of the test changes for different classes of respondents. In this study a reading comprehension test composed of 20 multiple-choice items is analysed with mixed Rasch model. Findings show that a two-class model fits the data best. After investigating class specific item profiles the implications of the study for test validation along with the contribution of the research to our understanding of reading processes are discussed.