In this mixed methods research study, the researcher investigated the difference between additive and subtractive bilingual education programs and student achievement. The researcher examined types of bilingual education and special language programs currently utilized in school districts located within the Education Service Center Region Two (ESC-2) located in South Central Texas and the passing rates of English language learners (ELLs) on state mandated Reading/English language arts and Mathematics assessments. The three main purposes of this study were to quantitatively and qualitatively explore characteristics of bilingual education programs currently operating in Texas ESC-2; identify characteristics of ESC-2 bilingual program directors; and examine how district level administrators used accountability data in bilingual program design and implementation. The study analyzed student academic performance data of ELLs enrolled in additive and subtractive special language programs, as compared to ELLs not receiving any special language services. The data was analyzed for significance using an analysis of variance (ANOVA). The findings indicate that additive bilingual programs, and the instructional strategies utilized, had a statistically significant effect on student passing rates on the state achievement test [F(2,6) = 15.89, p = 0.004]. However, the study did not find that subtractive bilingual programs had a significant effect on student passing rates on the state achievement test. The population of the survey included bilingual education directors, or otherwise responsible district-level administrators, from public school districts in ESC-2. The survey was matched to Academic Excellence Indicator System (AEIS) data obtained from the Texas Education Agency (TEA) for the 2009-2010, 2010-2011 and 2011-2012 school years. The qualitative component of the study allowed for the examination of factors influencing program choice/implementation by bilingual education directors. Respondent feedback indicated that 52% of bilingual education program directors continue to operate the same model of bilingual education or special language program that was in place before he/she began his/her tenure as Director of Bilingual Education without revision (status quo). Recommendations for further investigation into choice of additive program adoption may improve student academic achievement as measured by mandated accountability standards. Implications for theory and practice are discussed in the summary and conclusions. [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/en-US/products/dissertations/individuals.shtml.]