There is an interdependent relationship between academic proficiency and English language proficiency. This quantitative, correlational study examined the threshold hypothesis in relation to two required summative assessments for third--eighth-grade multilingual learners in South Carolina. Third-grade multilingual learners from a large school district took the South Carolina College- and Career-Ready Assessment (SC READY) and Assessing Comprehension and Communication in English State-to-State (ACCESS for ELLs 2.0) at the end of the 2021-2022 school year. Using the data from the two assessments, the following research questions were addressed in the study: How do third-grade multilingual learners' ELA scores on SC READY correlate to literacy composite scores on the ACCESS for ELLs 2.0 assessment? How do third-grade multilingual learners' reading scores on SC READY correlate to reading domain scores on the ACCESS for ELLs 2.0 assessment? How does the socioeconomic status of third-grade multilingual learners affect ELA scores on SC READY and ACCESS? The relationship between the two assessments was a strong, positive linear one as determined by Pearson's Product-Moment correlation results. A scatter plot chart was created using data points from the three correlation analyses to further affirm the outcomes. Of the 317 multilingual learners in the study, about one-fourth scored proficient on ACCESS, and one-third scored proficient on SC READY. The study determined that academic proficiency increased as English language proficiency increased. The study advocates for early intervention and intentional instruction for multilingual learners in order to reach academic proficiency and English language proficiency. [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.]