For high school science teachers working with students who are in the beginning stages of English learning, it can be difficult to engage English learner (EL) students in using language that is accessible to understand complex scientific concepts. Improving EL students' access to science education is an important component of diversifying professional fields related to STEM. Encouraging the use of students' home languages is a generally accepted strategy for science content learning (NASEM, 2017; 2018), but the recommendation as it stands lacks depth for practical implementation. The design for this study was a single, longitudinal, embedded case study which used a single group of individual students as the embedded units of analysis (Yin, 2003), sampled over four data collection points. The case study took place in a Physical Science and Language Development class that covered basic high school chemistry and physics concepts and incorporated language skills central to science and engineering practices. Over 33% of the student body at Taft High School (pseudonym) were considered EL students. The theory of social semiotics was used to frame how students were co-constructing meanings about the science concepts presented in the class. Student language was parsed into utterances and coded for language forms and functions. Emphasis was placed on STEM-specific language related to Explanations, Questions and Reported Speech (reading out loud from a science text). In addition to form and function codes, word counts were used to identify the most common words for each student per class. Results of this study show that student language use changed depending on the nature of the class topic, particularly related to incorporation of mathematical representations of science data. Student roles also shifted across classes as they engaged differently with different tasks. All students were able to utilize Spanish and English to participate in scientific sensemaking, particularly when they had resources such as a textbook and a manipulative object to refer to in their discussion. Implications include a need for more robust materials in students' home languages, fostering partnerships beyond co-teaching relationships, and further research investigating similar science education contexts. [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.]