The ability to comprehend science texts is not only an academic skill but a life skill. Currently, however, the majority of students across grade levels in the United States are reading below grade level "and" have science achievement below grade level. The text structure strategy, a reading comprehension strategy in which students are taught to use the structure of a text (e.g., comparison, cause and effect, problem and solution) to construct the main idea of the text, has been shown to be successful in improving reading comprehension. Therefore, the text structure strategy was implemented in grade 7 science classes to improve reading comprehension and science knowledge. The intervention included practice-based professional development, weekly instructional planning, modeling of text structure lessons in science, and adaptation of instructional materials to support the text structure strategy. This study investigated the efficacy of the text structure strategy in a grade 7 science classroom with four teachers and 169 students in a small, semi-rural district. The researcher collaborated with school administrators to provide teachers with practice-based professional development and ongoing in- and out-of-classroom support during the intervention. The study utilized a quasi-experimental pretest-posttest design. Results from paired t-tests showed that students significantly improved on science knowledge, reading comprehension, signaling word knowledge, and main idea quality. The text structure strategy in science has promise as an effective strategy to improve reading comprehension and science knowledge of middle school students. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]