This study examines the impact of minority language policy shifting from Mongolian to Mandarin Chinese on English test scores among elementary Mongolian-Mandarin Chinese bilingual students in Inner Mongolia, China. Utilizing panel data from 2018 to 2024, the research includes four cohorts of students from grades 3 to 5 at an elementary school in Hohhot City. The methodology incorporates descriptive statistics, two-sample t-tests, ANOVA, and mixed-effects regression models to evaluate the policy shift's impact on English performance. The analysis reveals a significant decrease in English scores following the policy implementation, with students exposed to the policy earlier experiencing more pronounced declines. The findings underscore the importance of early bilingual education for supporting third language (L3) acquisition. Significant variations in English scores are observed based on gender and grade level, with males and higher grades showing lower performance. These results underscore the necessity of maintaining robust bilingual education policies to support minority language speakers’ L3 learning and promote equitable educational outcomes. Future research should aim to include a more diverse sample, extend longitudinal tracking, and incorporate qualitative methods to provide a comprehensive understanding of language policy impacts.