With the gap between the highest and lowest-income Americans at its widest level in decades, some business schools are putting income inequality on the syllabus.

The b-schools at the Massachusetts Institute of Technology, Harvard University and Northwestern University are adding new courses and investing in research that probes income inequality at home and abroad. Some of the new courses consider remedies for inequality, while others focus on helping students market to consumers at the bottom of the wealth pyramid. As M.B.A.s...