What do I do till then? Let him play by lifting his fingers? ( Which by the way he tends to do. He has been experimenting on his own on the piano before he started lessons)
I teach rotation from the very first, since everything can and should be played with rotation you certainly don’t have to wait until Liszt,.
1. Demonstrating and having the student imitate you – both away from the piano and at the piano.
2. Actually moving the student hand (while he stays relaxed) so s/he feels what it is like).
3. And the most important one: find a situation in the life of the student where s/he uses the motion naturally and transfer the knowledge to piano playing. In the case of forearm rotation, you can ask them: “How do you turn a door handle?” If they go to karate lessons, asked them to show you a karate punch (it involves rotation of the forearm). You get the idea. This is a powerful method because they are not required to learn something new, but rather to apply something they already know to a new situation.
There is no lifting, the finger goes down, the key pushes it back up.
Again, rotation is just one movement – there are many others (hand shifting and backwards and forwards motion of the arm to accommodate the thumb and little finger are other important ones) – and most important: their co-ordination