As you can see here, a staggeringly high proportion of Atlanta University graduates were becoming teachers. As Serwer says, it was part of a larger trend in which “Jim Crow was funneling the most educated black minds into a very limited set of professions.”
This and the parallel set of facts for women is, I think, an unduly neglected trend in recent American life. A related point is that you tended to see relatively high-performing K-12 education systems in Communist countries. Jim Crow, patriarchy, and the economic policies of Fidel Castro are all ways to artificially increase the appeal of a teaching career relative to other options. This is not a good reason for a country to adopt Communism or arbitrarily exclude women from careers as lawyers or bankers, but it does mean that the expanded labor market opportunities for women and minorities over the past 40 years has been a substantial negative shock to the human capital of K-12 schools. The qualities that make someone the best 6th grade English teacher in the world probably aren’t identical to the qualities that make someone the best public relations executive in the world. But they’re not totally uncorrelated either. When teaching was the only thing many classes of smart ambitious people could do, it was easier to run a high-performing school.