One of the drawbacks that the foreign teachers presented was the fact that they usually prepare teaching materials ad hoc and only just before each class. Another was the fact that they tend to disappear after fulfilling their teaching obligations for the day, leaving no time for further teacher-student contact, thus adversely affecting the quality of instruction.
壞處是，外師通常只在上課前才準備教材，就上場教課，下課後就走人，沒有時間接觸學生，因此教學品質普遍不佳。