This article reports on the results of two studies on receptive and productive vocabulary knowledge of first-year English majors in an English-medium degree programme. The aim of the study is to answer these research questions: (1) to what extent do the receptive and productive vocabulary sizes of English majors increase after a year of instruction; (2) what is the ratio between the increases in receptive and productive knowledge; (3) do English majors achieve the expected threshold vocabulary size of 4.000-5.000 word families, after a year of instruction, that will enable them to follow lectures in English? In order to gauge students' receptive and productive vocabulary knowledge, participants in this study -159 first-year English majors -were given two vocabulary tests at the beginning of their first and second years of study: the Vocabulary Levels Test and the Productive Vocabulary Levels Test. The results indicate that: (1) learners' receptive vocabulary did not expand, whereas their productive vocabulary increased by 21 per cent; (2) their overall receptive vocabulary knowledge was larger than their productive knowledge and the gap between the two narrows after one year; (3) despite having received instruction, after a year, learners still lack the vocabulary threshold to meet their academic needs. Based on these results, the study reflects on the relationship between the content of the teaching materials used in class and the students' vocabulary knowledge. Recommendations aimed at informing teachers about the appropriate steps to take to approach language proficiency teaching are also discussed.