The authors evaluate the success of Arizona's program for English Learners (ELs) twelve years after the implementation of Proposition 203 to determine whether it meets the "third prong" test of Castañeda v. Pickard (1981), which requires a demonstration of the effectiveness of a program after its implementation. This study is a follow-up to Mahoney, MacSwan, Haladyna, and Garcia (2010) and evaluates the performance of former English Language Learners (FEPs) versus monolingual English speakers (EPs). The data is collected from the statewide, student-level database of student scores for Arizona's Instrument to Measure Standards (AIMS) for the years 2002-2013, effectively measuring the effects of Proposition 203 on the achievement of Arizona's ELs whose entire school experience has been conditioned by the new law. The overall research design was cross-sectional where proficiency levels on the AIMS were examined during post-Proposition 203 years. The results show that the difference between the two groups has grown over time, indicating that the state's achievement data does not support the conclusion that Arizona has improved educational outcomes for its ELs, failing the third prong test of Castañeda. Based on these results, the authors suggest repealing Proposition 203, as California and Massachusetts did for similar anti-bilingual education measures.