"Not a good fit" equals "Not flaming radical right enough." Probably your neutral books seemed dangerously logical, intellectual, and open-minded to them. You taught some students about Emmett Till, and with enough detail to inspire them to write about him. That alone would constitute a subversive act in the minds of the white-supremacy right-wing ideologues who are spearheading the charter school movement. I grew up in Chicago in the fifties, and my teachers were afraid to say much about Emmett Till. Big money interests are heavily weighted in favor of white supremacy myths, and their disciples are ever alert for "Communist" and "Radical" efforts to overthrow civilization. In the small, dark minds of these people, the peace of the world hangs on maintaining the myth of noble white people gradually civilizing dangerous Black savages. They think that classroom discussion of white-supremacy terrorist acts is so uncouth, so anti-white, so likely to incite a race war! You have performed acts of heroism, and done your part to make the world a better place. This is their loss, and some other school system will gain a wonderful teacher.