"I could not survive financially without the additional income," Gienapp writes in an e-mail message.

Gienapp says the job can be hardship. Many professors devote their summers to intense research in preparation for publications.

"It is an enormous handicap, since I have no extended time either to do research or write. In order to compensate, I have to spend more of the days I am not teaching on my own work, which severely limits activities with my family," he writes

For Damrosch, who also teaches English S-10b: "Major British Writers II," summer school wages can pay for research in other years.

"Some summers I may go abroad to do research. And some summers I am catching up [financially] like this," he said. "Financial motivation is a strong one. But it doesn't mean it isn't worthwhile doing."

According to Buck, many summer school professors manage to be prolific scholars even with the extra teaching commitments.

"The people who teach in summer school seem to do more than their share of writing and research," he says. "Teaching is time consuming. If it is not intellectually stimulating and you are not enjoying it, no amount of money is worth it," Buck says.