Good post. Traditionally , it was the Clubs that took these young men's development further after School. You look at one of the most successful periods in Australian Rugby through the 90's culminating in the 99 world cup and you are hard pressed to see many GPS boys as part of that mix. Fletcher Dyson was a John Paul College student , David Giffin a Redeemer College student , Damian Smith - Clairvaux, Dan Crowley , Mark Connors and Brendan Cannon all Lauries boys , John Eales and Dan Herbert - Marist Ashgrove , Ben Tune went to St Pauls at Bald Hills , Sam Scott Young - Townsville Grammar, Matt Cockbain was Country NSW (Coffs) as was Chris Latham (Narrabri) and then of course you had Tim Horan,Brett Robinson and Garrick Morgan from Downlands. Totai Kefu from Coorparoo High.
I am sure there may be others but the only guys I can think of off the top of my head that were part of the core from that era who were GPS lads were David Wilson (BSHS/IGS) and Jason Little (TGS)
But their real development and consequent opportunities came out of kick ass strong Clubs - Souths and Brothers especially through the late 80's into the early to mid 90's