Purpose: In 2 experiments, we examined the influence of prior knowledge and interest on 4th- and 5th-grade students' passage comprehension scores on the Qualitative Reading Inventory-4 (QRI-4) and 2 experimenter constructed passages. Method: In Experiment 1, 4th- and 5th-grade students were administered 4 Level 4 passages or 4 Level 5 passages from the QRI-4. Prior knowledge was assessed by key concept questions from the QRI-4. Interest was rated on a 5-point scale. In Experiment 2, 4th- and 5th-grade students were administered 2 passages from the QRI-4 and 2 experimenter-constructed passages. One general question was used to assess prior knowledge, and 3 measures were used to assess interest. Results: Prior knowledge as measured by key concept questions on the QRI-4 or a general question had minimal impact on passage comprehension. More important, only one third of the prior knowledge questions on the QRI-4 were related to a comprehension question. When these question pairs were analyzed, having prior knowledge was still not predictive of comprehension performance. Interest level had minimal impact on comprehension performance. Conclusions: This study's findings raise concerns about the usefulness of prior knowledge assessments on the QRI-4. Interest had little impact on comprehension performance. Educational implications are discussed.