Others have said it, I will agree: let the problem-solving take place between the piano teacher and the child. You can identify problems that you see in home practice and in motivation by way of letting the teacher know what's going on, but then leave it. If the teacher is any good, they will find solutions. And if not, you might find a different teacher who motivates your child.

The fast practicing, for instance, may be easily solved if the teacher gives the child a metronome and tells him how fast to practice. It will almost undoubtedly not be solved by parental hovering.

I agree with prev posters: forcing him will guarantee that he hates it forever. IMHO it would be better to change teachers, change approach, change instrument, change to social music-making rather than solo-- anything rather than turn him off to an entire art form.

DeeDee