This study investigates the effectiveness of the Tamil–English Bilingual Method on vocabulary acquisition among Tamil-medium higher secondary school students in Tamil Nadu. A quasi-experimental design was used, involving control and experimental groups (N = 30 each). While the control group showed no significant improvement in vocabulary scores, the experimental group that received bilingual instruction demonstrated a statistically significant increase from pre-test to post-test. The findings support the use of the mother tongue as a scaffold to enhance second language vocabulary acquisition. This method is especially relevant in low-English-exposure contexts like rural Tamil Nadu, where students benefit from Tamil support in learning English. Bilingual instruction fosters better comprehension, retention, and learner confidence, offering a practical approach for English language education in similar contexts.