The purpose of this study was to determine whether a dual language immersion program had a significant effect on the reading literacy achievement of Spanish and English speaking seventh and eighth graders who were in the program for three years. The research design was a quasi-experimental, nonrandom quantitative research using ex-post facto data. The instrument used for the collection of the data was the Arizona Instrument to Measure Standards, a standardized state test that is given annually to all students in Kindergarten through twelfth grades. The test assesses the students' mastery on the state standards in each of the core subjects of reading, writing and mathematics. To determine whether a statistical significance existed in the reading achievement scores of the adolescents two statistical analyses, t-Test and analysis of variance (ANOVA) were conducted on the reading scores of 30 adolescent English language learner (ELL) as well as native English speaker (NES) seventh and eighth graders who had participated in a dual language as well as 30 adolescent students in a similar school who had not participated in the program. The results indicated that the dual-language immersion bilingual program did not have a statistically significant effect on the reading achievement levels of adolescent seventh and eighth graders who were English language learners or native English speakers. The program did not harm the students' ability to acquire reading skills in English. In fact, the raw reading scores from the AIMS test of the students who had participated in the program indicated an average growth of twelve points over a one-year period, which is over three times that of the growth of their counterparts who did not participate in the program. Furthermore, 80 percent of the students in the control group demonstrated on average an increase of 28 points in their AIMS raw reading scores. By comparison, only 50 percent of the students in the control sample group demonstrated an increase in their AIMS raw reading scores. The recommendations for further research include exploration of the remaining three areas of literacy: listening, speaking, and writing skills of the NES adolescents as well as ELL adolescents who participated in a dual language program; and the study of the students' perception regarding the impact of the dual language program on the adolescents' literacy skills. [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.]