The study examines the Japanese EFL learners'vocabulary at the 1,000- to 6,000-word levels, using my revised vocabulary estimation test (hereafter VET). The study also examines the rank correlation in the success rate. The data are analyzed according to participants' grades and schools. The study attempts to identify words difficult to acquire even for advanced learners (university sophomores). Results show that the average vocabulary of students is much smaller than previously estimated by existing estimation tools. There is a statistically significant difference in the mean vocabulary size among students according to their grades and their schools. There is a relatively or rather strong rank correlation between grades and between schools in the success rate in answering at each level with few exceptions. There are four words whose success rates are less than 50 percent even at the 1,000-word level even for
university sophomores: two nouns and two verbs. I conclude that educators should recognize the fact that there are many words difficult for students to acquire in common regardless of grades or schools and should devise ways of teaching these words.