The purpose of this study is to examine the impact of native-speaking English teachers(NSETs) on the English language learning among Korean students at elementary and secondary schools. The survey responses from 16,059 students in Seoul area and their parents, along with the students'scores on an English achievement test were analysed. In an attempt to more rigorously assess the proper impact of NSETs, those variables that might affect English learning such as private lessons and students' family background factors were statistically controlled. Overall, the students' perception towards the usefulness of NSETs, tended to be less positive as they proceeded to higher school years. However, the results also showed that the more learning experience with NSETs was associated with higher scores in the English achievement test at all school levels. The proper effect of NSETs not contaminated by other nuisance variables proved positive for elementary and middle school students, but not for high school ones. This result could partly be attributed to the specific context of high schools in Korea, where virtually all the class practices center on the college entrance exam, and therefore NSETs are probably not considered of much help to the students' urgent needs. It was tentatively concluded that NSETs might play a more important role at lower school levels, and suggested that NSETs need to be re-allocated, with more of them assigned to lower school levels, for the sake of higher efficiency of the this educational policy and better result of English education in Korea.