There are many other science competitions. If he really likes science, do not give up. He may try other science related projects such as Google science fair, intel science fair, national science bowl, physics olympiad, biology olympiad etc. Do some research or talk to his science teacher and find out what else he can participate.
One time failure does not mean he is not good. Sometimes it is just bad luck. At the competitive level, every player is very strong. You need some luck to be the final winner. Just do not give up, the more you try, the better chance you will win in the end.