MarS,
I had never seen a soccer game, until the first one my daughter played in, at age 5. Other than her games, I think I have only seen parts of a handful of games. But I do try to help the coach, and offer to set up the net, or be a line judge. Even an inept volunteer is valuable.
Classroom teachers are the same. I felt a bit out of place the first few times I walked in to help, but after a bit, it got to the point that if I was going in on a day with a substitute, the lesson plan had me teaching the class, and the Sub helping. (Those were the days that the Kindergartners all learned that Dams on the Lower Snake River should be breached, cattle should NEVER be on Public Lands, and only people with Fat-Asses ride ATVs.

)
For Civics lessons, they learned how to write letters to the Legislature calling for adequate funding to meet state and federal mandates. (They all used crayons....

)
But, I can tell you (which kind of brings this all back to the original point of the thread), the big yellow bus that drops kids off at school each morning sure brings a hell of a challenge. From kids that didn't eat because there is no food at home, to kids with severe developmental limits, to kids that don't speak English ("American" for you Dubya supporters

), to kids with dads in jail, and other things.
And when you see what the teacher has to deal with that is NOT teaching, I think they are worth every penny of their $25k per year, if not more.