教训(jiào xùn) - lesson learnt the hard way; to tell off, to lecture in Mandarin

教训 (jiào xùn) is not a school lesson. As a noun it is the lesson a mistake teaches you, the thing you 吸取 or draw from a failure. As a verb it is what an angry parent does to a child: telling them off at length.

The classroom word is 课, and a single teaching session is 一节课. Say 今天有三个教训 and you have announced three separate dressings-down, which is a very different afternoon.

The verb use is always aimed at somebody with less standing, so it carries a whiff of superiority. 别教训我 is a real protest, roughly do not lecture me, and learners meet it in family arguments long before they meet it anywhere else.