What sort of info. are you looking for? Most teachers are union members. The union speaks for them and the school boards have to "play ball" to a certain degree. The whole "union" mentality begins in the schools of education at the university level. Call it "indoctrination" by the credit hour.
More importantly, the NEA is one of, if not the most, powerful lobbies in Washington. Surely the extreme number of delegates to the Democratic convention that are NEA members illustrates the hold the NEA has over the Democratic Party as well. Democratic candidates that oppose the NEA might as well not run. The NEA "buys" the loyalty of the Dems each year and the Dems cannot afford to do without their money or their influence.