He should probably be taught that microwave ovens literally use microwaves to heat food up and won't change the temperature of plastic or glass. I understood it when I was that age and if he is interested in science like it seems then he will listen.

Op, You should be happy you have a curious kid. You should find out what he or she is interested in and buy learning kits. Some advice from when I was a kid: purchase a tarp or similar material that can protect surfaces and tell them they can only take things apart on the tarp. My mother wasnt happy when i took things apart and stained the carpets. a large enough designated work area can save a few headaches and dollars.

Did it work?!

New type of engineering !

it could go either way a genius or a dumb ...

well, you got a 60$ science lesson. use it to your advantage. look up exactly WHY the microwave and thermometer did what it did. GOOGLE IT! and now you can get a new microwave. it could have been worse. youll laugh at this later, op. i promise. and now youve got excellent blackmail

And the bad news? You can't teach curiosity. Give your child a means to continue growing that interest and you'll have a successful kid in the making :).

Well did it??

I hope it wasn't a mercury thermometer.

Curiosity killed no one. He's still better than those 18 years old.