This study examined how three different pre-reading (or relevance) instructions led to different learning outcomes for middle school students reading science texts on the topic of sweetness. The first was a generic instruction to read for understanding. The second prompted students to form a holistic explanation of the topic of sweetness, and the third instruction prompted students to focus on the core scientific principle of the relationship between structure and function. The latter two were specifically designed to align with science disciplinary goals. A comparison of the three treatments found that the generic instruction and the structure-function instruction led to better learning outcomes, measured by recall, short-answer performance questions, and a traditional multiple-choice/short-answer assessment. A qualitative analysis of the data also revealed some small yet notable differences in the recall pattern of students, such as an increased recall of key ideas for the structure-function instruction. This effect was seen predominantly for higher-skilled readers. The results suggest the possibility that relevance instructions targeting core ideas may help to orient students to the key ideas and explanations in scientific text, especially for higher-skilled readers, and indirectly highlights some of the challenges for students with less reading competencies. Overall, this study provides greater insight into how middle-school students read science texts, the effectiveness of instructor-provided relevance instructions in promoting (higher-level) comprehension of science texts, and implications for teachers on how to use texts in science instruction. [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.]