I try to use Chinese as much as possible when teaching, but if I can't get through at all, English usually does the trick.
唉，其實有些人上課之所以不專心，是因為聽不懂；有的甚至需要同學的翻譯，才知道老師在講些什麼。所以我通常允許上課可以不太安靜。上課時我儘量用華語教學，但碰到溝通不了的，還是用英語解釋，這時往往一點就通了。