The purpose of this causal-comparative quantitative study is to examine the Maryland principals' role to influence the academic success of secondary ELLs. This study was conducted to determine if the principals' background knowledge, practices, and beliefs demonstrate a relationship as measured by a high school graduation gap between ELLs and all students. There were 39 principals who completed the Principal's Survey. Results from an independent samples t-test showed that the principals with less experience at their current school were statistically significant with a smaller graduation rate gap. A one-way ANOVA found that principals who used one instructional model had a smaller graduation gap than those who used four instructional models. An independent samples t-test revealed that the greater the principals' desire for family community engagement professional development, the higher mean graduation rate gap. The mean graduation gap rate was found to be smaller for principals who strongly agree that when teaching content to ELLs, teachers should draw on cultural experiences, heritage, and behaviors. Principals who promote language acquisition which provides native language support for ELLs to help them to learn academic content was associated with a lower graduation gap. Principals had a significant challenge in engaging parents and coping with a lack of resources. The results from this study will provoke further discussion and research to help serve the diverse needs of ELLs at the school, district, and state level. [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.]