Hello all, Claudia here,
Even though I don't teach French, today I would like to share with you a mnemonic my high school teacher gave us while I was learning French. It is really hard for students to learn when to use the verb être while using the passé composé. One thing my teacher used to do was draw a house on the board and tell us that the 'house verbs' were the ones that used être as an auxiliary. Of course we also had to remember that this would only work if the verb didn't have a direct object.
I hope you find this helpful!