Summer is over, and hundreds of students who spent the summer as interns for various public officials are heading back to school armed with new knowledge, skills, contacts, and a shiny line on their resume. They'll soon start working on their assignments for class. Meanwhile, the Office of the Mayor should work on an assignment of its own — finding money to pay next year's interns.

According to reporting by Michaela Winberg for Billy Penn, the 50 lucky students who get to spend their summer as interns for Mayor Kenney are not paid.

The mayor's office explains that the internship is an educational and developmental experience. The internship offers skill-building workshops — such as resume writing — and networking opportunity. The interns work on a project in a manner that is similar to a class.

The program does sound like a good opportunity — a gateway into public service. That is why it is a shame that low-income students for whom taking an unpaid summer internship is not an option are less able to take advantage of the opportunity.

There are very tangible benefits for an internship. According to the B.A. Rudolph Foundation, 51 percent of students who had one or more internships graduate with a job offer at hand compared to 17 percent of students who did not have an internship.

This is exactly the type of cycle that limits social mobility. According to a Pew Philadelphia Research Initiative, only 1 in 4 Philadelphia residents who are making a middle-class salary were born to parents making less. If you aren't born with money, you are unlikely to make money.

The mayor's office says that it encourages students to find external funding or ask their schools for college credit. Getting external funding is hard — only 10 of the 50 interns this summer had some sort of stipend, according to Billy Penn. While college credits sound like a benefit, they actually cost. Most schools charge students for every credit  — even credits that do not include a class, such as an unpaid internship. Half of the students in Pennsyslvania graduate with more than $26,000 in debt. When students are asked to pay for credits for unpaid internships, they are also asked to pay for the interest.

Due to the growing number of unpaid internships in for-profit entities, states such as Oregon and California cracked down on employers whose internships violated minimum-wage laws. In 2010, this action compelled the Labor Department to pay more attention to criteria for internships.

Government entities and nonprofits have more leeway for unpaid internships; still, in June, the U.S. Senate allocated $5 million to pay interns in the hopes of attracting a more economically diverse cohort.

Kenney says that he is in favor of raising the minimum wage — which the city can't do alone because of state preemption — and the city's requirement that contractors pay a living wage.  He should extend the same concern to students working for him.

The mayor has a full academic year to find wages for his summer interns. We hope he aces this assignment.