The ‘rule’ with Wh-questions is a bit more complicated than that.
If a fronted Wh-word represents the subject of the question, neither inversion nor Do-support is required.
Who is the man with the shovel? <<< Bob is the man with the shovel.
What keeps him going? <<< Whisky keeps him going.
If a fronted Wh-word does not represent the subject of the question, then inversion—flipping the subject and the finite verb in the verb chain—is required.
What is he digging? <<< He is digging a ditch.
Why is he digging it? <<< He is digging it to earn enough money to buy a bottle of whisky.
In Present-Day English, only auxiliaries and the verb BE tolerate inversion. If the finite verb is not one of these, then DO-support is required, to supply an auxiliary.
What ✲drinks he? <<< He drinks Jim Beam.
This requires DO-support:
What does he drink?
Rule 3 only started evolving some four hundred years ago, and there are still exceptions to it. For instance, it’s still possible to hear lexical have inverted without DO-support: “What have you in that bag?”
There are moreover questions in which the WH-word is not fronted: “You said what?!” or Bill Franke’s “Sez who?”
But those three ‘baby rules’ should suffice for common-or-garden-variety questions until your students are more knowledgeable.
✲ marks an utterance as unacceptable