The lack of use of the POH starts from day one of a PPL's training, the problem lies with the fact that the document forms part of the C of A of the aircraft. As such most operators are very reluctent to let the aircraft POH out sight because students have a habit of taking them home by mistake.
The trouble that results from this can ground an aircraft at C of A renewal time.
Part of my PPL training course is an aircraft technical quiz that is usualy given on the first day that the student has a flight canx due weather, it involves finding a lot of technical detail using the POH thus introducing the PPL student to the book at an early stage.