To prepare students for the complex, multidisciplinary problems they will face outside of the classroom, current reform initiatives advocate for the integration of content and practices from science, technology, engineering, and mathematics (STEM) in the science classroom. One approach, integrated STEM, uses the engineering design process as a vehicle for learning. However, these lessons can be challenging for students, so it is essential that science educators employ various teaching practices to scaffold student learning. One way to achieve this is through the use of written and oral discourse that promotes meaning-making. The studies in this dissertation utilize Legitimation Code Theory as an analytical framework to create semantic profiles of an integrated STEM unit and middle school teachers' implementation of integrated STEM lessons. Specifically, we analyze the semantic gravity, or the extent to which meaning is rooted within the context it is acquired in, to map and identify semantic patterns that may promote or constrain meaning-making. The results of these studies indicate that Legitimation Code Theory can be a useful tool for developing and examining integrated STEM curricular materials, evaluating teacher discourse during the implementation of integrated STEM lessons, ascertaining how teachers are integrating multiple disciplinary discourses, and identifying areas where teachers may benefit from additional support as they learn to implement integrated STEM. [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.]