When all my friends and class mates were at the graduation ceremony / party, I was in school!
That's because I was in Japan as a foreign exchange student! I technically graduated the January before everyone else and then left for Japan, and they weren't going to do a special ceremony for me. And with the difference in time, when they were doing their things in the afternoon, I was in school!
But, my friends and family did a special party for me in January, so that was nice! It was a "surprise" party, at my house, with a bunch of my friends. Then later, my parents took me out to dinner to Black Angus.
Congratulations to your son!!