SAN FRANCISCO — For select students at top law schools, summer associate programs can be a months-long wooing party, as firms spoil their recruits with cruises and cushy salaries, with some work experience thrown in.

In the Bay Area offices of Duane Morris, the arrangement with law students is slightly different. The firm hosts externs at its San Francisco and Palo Alto offices year-round, drawing 3Ls from the University of San Francisco, Golden Gate University and Santa Clara University School of Law. The Philadelphia-based firm also runs a summer associate program but does not place any in its Bay Area offices.

Externs generally pay tuition to their law school and receive academic credit for their participation in the program. Though externships in public interest law have become a common offering at law schools, placements at private practice firms are novel—and have drawn some criticism from those who say the for-profit firms should pay students for their labor.