If there is any way you can miss some school to go, I think in the long run you will be glad you did it. Jack mattered to you. This is his last day. I have often felt that it is the little things in life that will make it best remembered. Nobody remembers all the days of school they went through. That's just something you have to get through to make the goal of a degree, certificate, or diploma. But you will not forget Jack's funeral, I bet.
I have a friend who is 65 now, and he told me a couple years ago that when he was a young man raising a family he never thought friends were very important. He said that now he is older and an elder in his church, he often is the only person standing at somebody's grave for a funeral. He told me he is afraid that when he dies nobody will be standing there, just like those folks whose graves he is presiding over now. It bothers him to think of dying alone.
Time is fleeting. If you think he matters enough to your values of what really is important, go to his funeral.
We have to become creative problem solvers, not just tolerant burden barers.