The purpose of this sequential mixed methods case study was to explore the role of a teacher's attitude towards Sheltered Instruction Observation Protocols (SIOP) and how those attitudes affect the program's effectiveness. SIOP is a program designed to mitigate the effects of limited English proficiency and promote equal access to the curriculum for the English language learner (ELL) to improve their academic performance. ELL students in one state are experiencing a significant educational achievement gap, and limited language proficiency is an obstacle that can be a contributing factor to underperformance. All the ELL 5th grade teachers in small Texas school district were included in the study. Following processes outlined by Hatch, qualitative data from surveys, interviews, and classroom observations were sequentially coded and analyzed to classify teacher attitudes toward SIOP. The results of the qualitative component was used to identify the two comparison groups of teachers, one group of teachers had a more positive attitude towards SIOP and the other group had a less positive attitude towards the program. Next, independent sample t tests of the district's 6 week reading and math exams were used to compare the academic performance of students across the two teacher groups established in the first phase of the study. The results of the t tests comparing mean academic performance were not statistically significant. This awareness can lead to social change in the area of improving academic performance for these students by helping to inform meaningful professional development and promising practices for teachers. [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.]