My concern is over his home machine being cracked, not the school administrators. If they want to be idiots, they will be idiots no matter what he does.

UPDATE
There is some truth to what dws says, far too many school officials these days seem to be petty tyrants and really don't like dealing with kids who can show them up. But still if you are connecting to your machine over the net, there are good reasons to use ssh rather than telnet.