Actually, the concept of charter schools began, largely, with the late AFT president Al Shanker and with Diane Ravitch, who has now become an outspoken opponent of charter schools and privatizing. Their original idea was to set up charters as independent laboratory schools, using tax funds to develop ideas that could then be transferred to the public school system. What neither of these idealists considered became obvious to profiteers who quickly saw charters as a means to transfer public school funds into their own pockets. At first, this profit margin came from lowering teacher benefits and wages. The. Then they discovered they could over bill for "improving" the existing, older school buildings they were given. The profiteers hit a ceiling when asked to prove their schools were doing better than public schools, which they were hard put to do, even after culling better students and rejecting special needs and ESL students. This is where the testing mania came in, under the aegis of Pearson and other companies. The beauty of the testing craze is that it is so low-cost, basically just producing tests and test prep books, and the extremely high price they could charge states like New York.
Shanker was also an early proponent of testing, through a now forgotten set of ideas known as "mastery learning." I developed some articles for Shanker on this, but since it was all non-profit, it went nowhere. Anothe reason why it had to go was its emphasis on teachers as partners in test development..
I had my differences with Al Shanker, but he was a socialist organizer while at U Illinois, and never lost his idealism. He honestly thought that the capitalist system could accommodate the kind of non-profit innovations he and Ravitch promoted. As a classic social democrat, he believed that the market system could generate profits that would then be directed to the common good. In my conversations with him in his later years, he sounded much like West German social democrats - and that included a blind support for US military dominance and an unrelenting anti-communism. Old time socialists, like his idol Norman Thomas, often followed this somewhat tortured ideology. (In fact, Shanker was instrumental in having a NYC public school on 34th Street named Norman Thomas High School - that failed too, and was closed last year.)
So, there were new ideas at one time in teacher unionism, but founded as they were on a blind faith in the free market system, they were soon distorted by those who see a chance for monetization in every human activity.