Oh I honestly think it's a pretty huge amount. This is just my experience. We had to test every year in Washington and almost half the kids that would show up for the test would end up failing it. The test was there to help gauge where the HSers were in learning. I don't know if anything was done about all the kids that failed. Honestly they failed because they couldn't read. We were in a big HS community and my mom turned in lots of moms and more recently a friend of hers. She had her 16 yr old daughter while her mom was on vacation and the kid couldn't read for SHYTE! Mom did some digging and all the kids were in the same boat. I'm not sure why they didn't feel it was necessary to help their kids learn to read. However they did it for the cause in my opinion. It was a big cluster of look how great I am my kids will not be tarnished by society. Nope instead they'll be pissed when they can't even fill out an application. but hey if you're going to be a farm hand for life... go for it.
True. I think parents do not always realise they masking a choice for a cause when they do it. Lives are messy. You can believe schools should be dismantled, have a kid who might thrive in school, but know the local schools are awful. Are you keeping your kid home because it is your cause or because the local school is horrible?
Same is true from the other side. You might believe kids belong in school, yet have a child who is struggling despite attempts to fix it, but most of your kids friends are at school. Are you keeping kids in school because that is where you believe they should be or because the pros might outweigh the cons? so hard to know!
At the end of the day, though, I think there are parents (not a huge amount) who are so em-meshed in a cause that they do not see *their* kids.