Science presents many challenging topics, and incorrect prior knowledge of them often interferes with learning. Research has demonstrated that refutation texts promote conceptual change learning by helping readers abandon scientific misconceptions. Little is known about the factors that influence knowledge enrichment, the learning that ensues when students have incomplete knowledge of a topic. The purpose of this study was to compare the impact of these two types of prior knowledge on science text comprehension. Participants were 28 high school students (14 to 15 years) who completed assessments of vocabulary, reading comprehension, epistemological beliefs, self-efficacy, interest, and prior knowledge of 4 science topics (2 misconception, 2 incomplete prior knowledge) on Day 1. On Day 2, participants read 4 science texts (2 refutation, 2 expository) and completed tests of comprehension. Results demonstrated that epistemological beliefs moderated the increase between pre- and posttest scores regardless of the type of prior knowledge. Knowledge enrichment was more than 2 times as likely as conceptual change, which required a minimum level of epistemological understandings. Although refutation texts rarely led to conceptual change, they contributed to knowledge enrichment more often than traditional expository texts did. Future studies should investigate the impact of non-textual factors on conceptual change and knowledge enrichment in science. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]