Textbooks are a crucial tool in English as a foreign language (EFL) contexts where out-of-the-classroom use of English is minimal. Vocabulary is an essential component of language learning; thus, EFL textbooks should sufficiently represent vocabulary needed for students' academic success. Due to the growing demand for English proficiency locally and internationally, Bangladeshi EFL textbooks' lexical coverage is examined to determine if vocabulary input is aiding students in their K-12 education and their transition to higher education. A corpus-based analysis of the Bangladeshi K-12 textbooks' vocabulary has been conducted, and the vocabulary of university textbooks is compared to the K-12 vocabulary. Results demonstrate that the transitions in academic stages are not easy, as the lexical input found in early-grade textbooks leaves significant gaps in vocabulary found in textbooks of the later grades, and similar results were found in the transition to tertiary levels. Pedagogical implications and recommendations are also discussed.