It's not that organizations like the NEA don't try, and the AFT to a much lesser extent, but they're just not successful in their efforts. Indoctrination in schools in a free society doesn't work. If it did the Catholic Church wouldn't be facing empty pews on Sunday. Where are all those graduates of Catholic schools in the 50s and 60s and 70s? More than half are not there or are just sprinkling Catholics. And no it wasn't Vatican II since most of these folks never saw a Latin Mass.
School districts and teacher unions may be trying to spread their ideology, but I have little fear of them being successful.
you say indoctrination doesn't WORK? Are you aware of just how close the Bush/Kerry vote was? Kerry's 50+ million votes should SCARE YOU TO DEATH and get you active on your local school board campaigns. It's at the school/local level you can make a huge impact. Texas just had a huge victory in insisting its textbooks referred to a man and a woman being the partners in marriage. ACLU had a fit...tough!
Math must be understood to be learned. Dogma can be learned without understanding. That's why young adults become more conservative as they get older. Their experience in the real world contradicts what they learned in school. Some will cling to school dogma uncritically, because a change in worldview would involve pain. Others will reject what they were taught.
The mechanism of modern schooling is diabolically ingenious. The most powerful lessons of schooling are absorbed rather than learned. They are the lessons of context. The following essay summarizes the method brilliantly.
The Seven Lesson Schoolteacher
Also worth reading: The Underground History of American Education