I'm a school teacher in Macon, Ga. I had never heard the usage of the preposition "on" in this context until I started teaching at an inner-city school. My principal, vice-principal, academic coach, and the superintendent of school all use this vernacular. It is very common in the educated African American community of middle Georgia. It drives me nuts. It changes an adverb into the noun of a prepositional phrase modifying a verb. If I had hair, I'd pull it out.