Don't know if it still applies in Auckland but the problem used to be that at a younger age the school played their games at say 9am on a Sat. morning and the club played at 1pm. Problem was that as the players got older their school games were played later. I had most of my club players playing at 11am and they then had to rush to the club game at 1pm. This was physically hard on them and some had heaps of pressure put on them to flag the club.
All this would have been solved if the schools played their games mid-week. I spoke to Johnny Morris about this when he was headmaster at Auckland Grammar and his reply was that it will never happen. I even had a couple of outstanding players who never told anyone at school that they played club football as they knew what would happen.