Because of their positions and age most students are very diligent and feel particularly embarrassed when they can't answer a question (which are numerous) from the professor.
「很多學生進來後就發現，這兒可不好『混』，校方對他們的要求和正規研究生一樣，所以該補考的就要補考，該『當』的還是會被『當』。」