You’re right, the teachers at all levels are high on the list. But the media are the ultimate political police. People talk about the judiciary legislating from the bench but it wouldn’t happen if the media did their job. Nor would the teachers expouse their indoctrination if the media neutrally did their jobs.
It is the media that people will hear,read, and see their entire life,whereas the indoctrinators(teachers?) only get them for 12 or 16 years.
The relentless media drumbeats for more government control and the concurrent media rejection of all traditional Judeo-Christian Western values both energize the statists and discourage the freedom loving.
Plus the press which this nation's founders envisioned as a check on government abuses has become a cheerleader and co-conspirator in the very misdeeds of government.
The only part jocon307 got wrong is that it's not just teachers unions, it applies even more in higher education than in public K-12 (though that's changing). In fact, that's where this all began -- Journalism Schools. Then it spread in both directions, to engulf the media and other departments in our colleges and universities. It wasn't until both areas were under leftist control that they began to spread downard into highschools and elementary. And, as you say, it couldn't have been managed if they hadn't already had the media in their back pocket.
One of the more worrisome aspects of this control is that the Left also has the Law Schools --- all of them. Take a couple seconds to think about the implications of that.
It's no worse than control of the media or the rest of education, but it's almost bad enough to count as the snake's third head.