Really? Granted I only flew from the one school whilst doing my PPL at MB, but I didn't realise that most schools had this sort of policy.
I can understand wanting an initial check done of course, regardless of how many hours you've got. That makes sense for the school and insurance. I just would have thought once you had been seen to be compentent by an instructor, you wouldn't have to re-prove your competence each 90 days (assuming of course your maintaining your legal requirments for currency).
After gaining my PPL I flew from that school consistantly 5 or six times a month for 10 months without a check from one of their instructors.
Oh well, maybe I got lucky.