The best reference I can recommend would be Eric Raymond's "How To Become A Hacker" : http://www.catb.org/~esr/faqs/hacker-howto.html The key point the article points out is that "The basic difference is this: hackers build things, crackers break them." The teenage thrill of breaking into computer systems is certainly exciting but perhaps he will be even more enthusiastic about learning to be curious about how things…
That might both give him some new ideas, as well as show who is really considered important. For example, I always thought lcamtuf (http://lcamtuf.coredump.cx/) is a great example of a hacker of many skills (photography, network security, fuzzing, constructing robots with own 3d printer and many more random ideas). I guess you just don't have time to be a script kiddie if you have enough good ideas of your own...
Just make sure he finds securityfocus before he finds cDc :)
On the other hand you could let him know, that notifying the school officially about the security problem may be a bad idea. Typical teachers are as likely to say "thanks", as "OMG hacker! security audit to make sure you didn't change any data will cost X$/h - your parents are paying for it and you're suspended".