In theory, the South African government advocates additive bilingual education over subtractive bilingual education. However, this study shows that subtractive bilingual education supersedes additive bilingual education mainly because the official African languages of South Africa are being marginalised and not utilised as languages of teaching and learning in schools. The majority of isiZulu speaking learners in KwaZulu-Natal are underperforming academically under a subtractive bilingual educational system. The findings of this study acknowledge that there are numerous contributing factors to this problem, but the most obvious is that isiZulu speaking learners are compelled to write their examinations in English. This study employed a triangulation approach where various literary sources were consulted to illustrate how English has emerged as a dominant language on the local and global stage, and how this has affected the status and use of minority languages. Qualitative approaches were used to gather data from Grade 10 to 12 isiZulu speaking learners who attend the so-called 'Black schools' in the district of Pinetown, in KwaZulu-Natal. Questionnaires and experimental tests were used as the main instruments for gathering data from learners. One-on-one interviews were conducted with educators and other relevant stakeholders. The observation technique was also utilised to monitor the behaviour of isiZulu speaking learners in both affluent and previously disadvantaged schools. By examining Cummins’ interdependency hypothesis (1979, 1996 and 2000) as a theoretical framework, this research study has proven that the continued use of English as the only language of teaching and learning in South African ‘Black schools’ has a negative impact on the academic achievements of the KwaZulu-Natal isiZulu speaking learners. The study, therefore, calls for the introduction of a language policy that will promote dual bilingual education where both isiZulu and English are used as the languages of teaching and learning throughout the KwaZulu-Natal isiZulu speaking learners’ scholastic years. The study has proven that this approach to education will facilitate better understanding of the subject matter and thus curb the high failure rate, especially in the so called 'Black schools'. / African Languages / D. Litt. et Phil. (African Languages)