This quantitative research study analyzed the effectiveness of Section 504 plans on academic achievement as measured by the Scholastic Aptitude Test (SAT), State of Texas Assessments of Academic Readiness (STAAR), and graduating grade point averages (GPA). There is limited research on the effectiveness of Section 504 plans and academic achievement. The study employed a quantitative ex post facto research approach to compare the effectiveness of Section 504 plans on students who graduated from seven high schools in 2017, 2018, and 2019 from a North Texas public school district. Results of dependent and independent t-tests of the data resulted in mixed results on the effectiveness of Section 504 plans on academic achievement. The study reinforces the importance of providing accommodations and supports to students with disabilities no matter how early or late they are initiated during a student's PreK-12 education. This study offers data to inform decisions made by educators, parents, and lawmakers as they consider policies, practices, and procedures for the development and implementation of Section 504 plans for students in our public-school systems. Implications for practice as well as future research are discussed. [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.]