how many students per teacher is there usually in a privite aircraft school?

Answer 1

Now that is an open ended Question. I have seen schools where it was one to one during slow periods and seen other schools where there were 30 students assigned to a teacher.

Normally there at a busy school there are between 20-30 per instructor during classroom time. While in the plane I have never seen more then 2 students per instructor. One flying and one in the back observing.

Answer 2

For classroom work One teacher can take care of 12 to 20 students.
For "briefing" type of training 3 students per teacher.
For flight training, 4 to 6 per instructor.