...but all the useful things: relativity, quantum mechanics, and chemistry that doesn't involve playing with little balls, don't come until second year university...
Not always true. I'm 15 and I've been over relativity and quantum mechanics in school (2 years back). Never chemistry though oddly enough. Perhaps I'm deemed a maniac by the administration and would use anything learned in chem to build explosives or powerful acids. Also, been an atheist for several years now. (5) Anyway, as long as he doesn't do that Gkd buried the bones crap don't worry about it.
Oh, and if he tries to tell you that the earth is the absolute center of the universe and does not move, kill him or scuttle him into a time machine bound for 800 AD. Just make sure he winds up in Europe. You might seriously ruin a culture if you don't. If he tells you the earth is flat and that pillars push it up to produce gravity, don't even send him back in time or kill him, just laugh.