If a teacher teaches more than three children, learning will be difficult or slow.
But this kind of teaching also has the advantage that children are more interested in studying together.
The best way to learn is to find a good teacher who is very professional, responsible and understands children. Of course, this kind of teacher is hard to find.
This kind of teaching method is usually once a week, and then every time parents watch the teacher give lectures, so that parents will know the progress, children's situation, specific practice methods and so on. And it's easy to go home and tutor the children. And a good teacher must make children like playing the piano very much.
In addition, if you want your child to have more contact, you can let him participate in some small performances and competitions. What matters is what you can learn in the process.