This study explored the long-term academic impact of Two-Way Dual Language (TWDL) programs on both English-dominant and Spanish-dominant Hispanic students in a high-density Hispanic area. Specifically, it compared their academic performance in English Language Arts (ELA) and Math over a 3-year period to that of students enrolled in traditional English-only General programs and Transitional Bilingual Education (TBE) programs. One key focus of this research was examining whether TWDL programs can maintain their effectiveness when the traditional 50:50 balance of native English speakers (NES) and minority language speakers is not met, substituting English-dominant Hispanic students for NES. The findings demonstrated that TWDL programs have a significant positive effect on ELA achievement for both English-dominant and Spanish-dominant students. TWDL students consistently outperformed their peers in both General and TBE programs, with substantial gains observed in English-dominant students, who showed the most significant improvement in ELA scores across all grades. However, Math performance declined over time for all groups, despite TWDL students maintaining higher overall Math scores than their peers in the comparison programs. This study highlighted the flexibility of TWDL program design, showing that substituting English-dominant students for native English speakers can sustain the program's effectiveness. In areas where enrolling enough NES is challenging, particularly high-density minority language areas, TWDL programs remain feasible and successful. The research aligned with Cummins's Thresholds Theory, which states that balanced bilingualism leads to cognitive and academic advantages. These findings have implications for the design, expansion, and implementation of bilingual education programs, especially in high-density minority language communities. The study contributes to the limited body of research on the long-term academic outcomes of TWDL programs in high-density Hispanic areas, providing evidence that such programs offer an adaptable and effective model for improving academic success among Hispanic students. Further research is recommended to explore interventions for improving Math performance within TWDL settings. [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.]