This was always an argument at Wests i remember. Some schools wouldnt release their players to Wests saying they had to play for their school sides, so Wests went to CF and asked why the schools were allowed to play club football. Back when i was at Wests we played Wellington Col, St Pats, Hutt High, Rongotai, Scots... etc. And when I was at Tawa, the school mixed freely with the Tawa club, so you had college players and players from outside the school playing in the same sides (except for the Youth grades, they stayed as school only).
And in Cap Reserve Miramar's 'Reserve' side was Wellington Coll First XI. (i say 'Reserve' because their Reserve side was actually their Prem side, with their top side playing National League)