The purpose of this study is to diagnose how correctly and appropriately Korean non-native speakers of English can use determiners (mainly articles) and to seek pedagogical implications for English teaching by comparing 'determiner' error frequency in the free writings from two informant groups: college freshmen as English learners and middle and high school English teachers as expert users of English. The errors of these two groups are investigated in terms of eight types. This study focuses on the similarities and differences in frequency of their error types and how the properties of these errors should be treated in English teaching in Korea under the current coexistence of localized world "Englishes".