First of all it takes 2 to tango.. I hope the girl also gets in trouble too, she is the reason the parents freaked out.
"Courting beyond hand holding" is not really allowed/ encouraged in schools, but it still happens.. It is just not the place to behave like that. It just seems trashy.. Also no one wants to see it.. Let your son know that if he does not want to see his parents making out in public, then guess what? No one wants to see teenagers doing it either..
The girl should have called her parents and told them she was running late or was staying after school. Your son should have done the same thing.
Teenagers want to spend time together and during the school day, this is not always possible.. I suggest if they want to spend time together, it should be at the girls home or your home, ONLY while a parent is present..
I am not sure what his punishment should be since it was the first time, But what ever you decide, let him know that this behavior will not be tolerated and each infraction will bump up the consequences..
Most parents,. take kids off of the computer (except homework) and texting for a week.. So maybe till sat?
Also have very specific expectations for his after school activities. He must call you and let you know where he is going to be when school lets out. Then another call for each place he goes after school.. Let him know it is not so much that you are trying to be in his business, but for your peace of mind or in case of emergency, you need to know where he is, just like you will let him know when you are out and about..
Let him know since it is just the 2 of you, you need to look out for each other.