The school may get upset with kids opting out. If all of the bright kids opt out, then the school's scores will drop (and thus the school ranking will drop).
Our HS got angry with kids a few years ago because some of them decided to "Christmas Tree" (make a pattern on) their answer sheets. Made the district drop from third in the state to sixth in the state on the mandatory state test.
Six hours isn't that much. I'm more concerned with mandatory PE where my eldest was stuck with idiots who didn't know that you needed to dribble the basketball. And then was chided when she stole the ball from these kids and scored. My kids are involved in year round travel sports. They don't need PE, but all of us are stuck with plenty of mandatory things that are a waste of time. It is a part of life.
