The study attempts to examine the effects of CALL-based vocabulary learning with a special emphasis on learners\u27 vocabulary levels and the potential effects of vocabulary practice. It also focused on how the effects were influenced by learners\u27 proficiency differences. Based on an earlier study (Kawauchi, Kamimoto, & Nagasawa, 2005), the following two research questions were examined: (1) Is it possible that learning vocabulary of one or two ranks higher than learners\u27 levels can increase the size of not only the vocabulary they studied but also the vocabulary of lower ranks? (2) Are there any differences between upper level learners and lower level learners? A total of 88 first year students were required to do an extra study of vocabulary practice using a CALL program, Power Words. Their vocabulary level was judged Level 1 by the diagnostic test attached to this program. 55 students (Group A) were asked to study the vocabulary of one rank higher (Level 2) than their current level and complete that level by the end of the first semester. Similarly, 33 students (Group B) were asked to study and complete the vocabulary of two ranks higher (Level 3) than their current level. 49 students of Group A and 29 students of Group B fulfilled the requirement. The present study focused these students to investigate the research questions, using pre- and post-tests. The results with Group A showed a significant increase at Level 2 and also at the lower rank vocabulary of Level 1. They also increased their vocabulary size at Levels 3, 5, and 6. However, these effects were found mainly in the lower level students. On the other hand, Group B showed a significant increase of Level 3 which they studied, but no effects were found in the lower rank vocabulary. This increase was, in fact, found in the higher level students. Based on these findings, some pedagogical implications are also provided
