"Perhaps the most outstanding show in educational radio, offered as a teaching supplement; the equivalent of a half-hour course, often dramatized by radio's top actors."It began in 1930 with little fanfare, but quickly gained popularity with schools. Positive reviews from 35 early-adopting schools helped spread the word. It was the first educational program designed for schools. It was a 30 minute program that ran on Tuesdays and Thursdays weekly. the program was not made up of voice actors. it was comprised of educators. It taught classes in history, literature, civics, art, music, and biology. A program might explain how pearls are formed, or folk music, or life in a foreign country. The equivalent today might be screening a documentary in civics class. More here.
In 1940 the events of WWII compelled supervisor Sterling Fisher to syndicate the program abroad. It made it to atleast 15 other countries. Although it was not overtly political, newsmen like Edward R. Murrow guested on the program. It ran for 18 years only ending it's run in 1948.
While purely educational programming was rare, the "School of the Air" branding was used by a number of stations individually. Florida and Oregon has state-funded programs with the same name, as did stations WHA, WCAL, WOSU, and WLW, all broadcast programs hitching a ride off the successful branding and CBS let them. But the CBS School of Air was the leader. Late in the game they rebranded as "the American School fo the Air" to better distinguieh the program.
But it ultimately why the confusion arose becomes clear. In 1924, when general Mills lanched a cooking show on the radio it was called the "Betty Crocker Cooking School of the Air." In 1930, the branding was already in use. It was never theirs to be co-opted. It was stolen, or else the terminology had already entered some kind of general usage.