The purpose of this study was to measure to what extent additive bilingualism, a process where students learn a second language while continuing to develop proficiency in their first, can enhance the Cognitive Academic Language Proficiency of students. A secondary purpose of this study was to explore if additive bilingualism can enhance subject matter comprehension. The support of additive bilingualism in the online course was done by means of embedded instructional strategies that were borrowed from the practice and research already done in face-to-face courses. Before this study, there was no research in applying these instructional strategies to online courses. Significant differences were found between the treatment and control groups on their English proficiency and subject matter performance. The results indicate that providing instructional strategies that support additive bilingualism enhances Cognitive Academic Language Proficiency and subject matter comprehension. This study also points to directions for future research in this field and discovers important implications for teaching, educational administrators, and commerce.