A new report out from Georgetown University takes a look at return on investment at colleges. Key findings: public colleges returned more on investment over 10 years than private nonprofit colleges did, but private institutions returned more over 40 years. The average private college grad can expect to see an economic gain of $838,000 over 40 years, the report says. Public college grads can expect $765,000. For-profit college graduates can expect $551,000.