Don't, whatever you do, do as I did when I refereed my first schools match a few years back and agree not to show cards because "they're great lads, never give any trouble and if you have any problems we'll take them off and they will be dealt with by the schools".
I was asked to referee the first team of the local private school against Eton; it seemed a great gig - £40.00 match fee with lunch and a couple of beers thrown in and only three miles from my house but as I had agreed not to show cards and to let the school internal discipline deal with things, it turned in to a complete nightmare - constant dissent from both teams, tackles getting progressively worse and, as I couldn't caution, I had no way to control things apart from stern words or for players to be removed which, as none of the offences were straight reds, was tricky particularly as by the end I probably could have sent most of the players from both teams off for two yellows. I was very inexperienced at the time and would probably have handled things better now but without at least the possibility of a yellow your match control can suffer very badly...
My advice: referee exactly as you would any other game. At its best schools football can be fast, skilful and great fun to ref and usually far fewer parents than youth football (which is always a bonus).
