CTPE, there's been an attitude among many parents of talented rugby juniors to treat these institutions as "rugby finishing schools". The northern beaches, north shore and the greater north-west of Sydney have traditionally been strong rugby areas (Eastwood have, what, seven feeder village clubs, and Wahroonga Tigers is the biggest junior club in Australia). Parents, mostly fathers, want their little champion to go as far as he can in Dad's favourite sport, and to this end the parents make enquiries at King's, Joeys, Knox, Barker, Scots, Newington, wherever, when young Sam/Mark/Phil makes the district under 14/15 rep side. In my experience the vast majority of late entries in these circumstances pay full freight. There's also another imperative in these late enrolments: a helluva lot of parents can't afford to pay private school fees for six years, hence the couple of boys in Joeys Ones last year who had older brothers precede them. Apart from the affordabilty issue there are legions of mothers out there who are reluctant to send little Sam/Mark/Phil off to boarding school aged 12.
A specific example: when my young fella started at one of these institutions two blokes from my year also had their sons commence at the same time, but in year 11. One couldn't afford six years and the other's mother wanted him at home until he was 16; neither of these boys made the First XV. There are many reasons why good rugby players appear in years 10 and 11 apart from blatant poaching.