You are so damned PC-institutionalized on this issue that you probably lean left when you walk.
Pure southron myth. Sunday schools for blacks were not uncommon in the south. Most southern churches felt it their duty to bring Christianity to the slaves. Jackson's Sunday school was far from the first and he didn't build it, it had been established at that church years prior to Jackson's joining. And you have to remember that some of the slaves at that school belonged to Jackson himself.