On the list of edicts you never want to hear in childhood: “You need braces,” “Brussels sprouts for dinner” and “Get ready for summer school.”

While most children come to see the merit in straight teeth and cruciferous vegetables, few ever look warmly at summer school. And why would they?

Summer school is still perceived as a punishment for failing to get it right during the regular school year.

Ensconced in a hot, stuffy room while their pals skateboard, jump in the pool or haunt the mall, students stuck in summer school see the classroom windows between them and freedom as thick and unyielding as prison walls.

But a quality summer learning program can play a role in closing the gap between low-income students and their middle-class peers, according to a new study released today by the RAND Corp., “Making Summer Count: How Summer Programs Can Boost Student Learning.”

“Summer learning loss is very real,” study co-author Jennifer Sloan McCombs said. “Each fall, students on average perform a month behind where they did in the spring.”

The loss is most pronounced among low-income students who are less likely to regain that lost ground.

“While all students lose some ground in mathematics over the summer, low-income students lose more ground in reading, while their higher-income peers may even gain,” according to the RAND study, funded by the Wallace Foundation.

“Most disturbing is that summer learning loss is cumulative; over time, the difference between the summer learning rates of low-income and higher-income students contributes substantially to the achievement gap,” the study warns.

In a conference call, co-author Catherine H. Augustine discussed the findings, which focus on what successful programs are doing to entice children to attend and how systems can fund such programs despite budget shortfalls. “Getting kids to attend is not always an easy sell given the long-standing stigma of summer school,” she said.

To combat the stigma, Augustine said districts are combining a morning of academic classes with enrichment activities, including arts and kayaking.

Those are the sorts of enticing activities that middle-class kids often experience in the summer, either through family vacations or pricey summer camps.

Children’s camps in Atlanta have gone well beyond roasting marshmallows and making potholders; young campers now make robots, documentary films and gourmet meals.

Using a combination of funding sources, school districts are recasting summer school to provide equal amounts of summer and school because they understand that programs will not succeed if children don’t show up.

And these programs want to reach beyond the small pool of children at risk for retention if they don’t attend summer school to the much larger pool of students who could simply benefit from additional math and reading.

So districts are incentivizing the programs, presenting kids with a good reason to study fractions and literature in the morning so they can participate in tantalizing activities in the afternoon.

Baltimore had a waiting list for its summer learning program last year that featured swimming lessons by Olympian and Baltimore resident Michael Phelps and his swim school, Augustine said.

Pittsburgh schools last year launched the Summer Dreamers Academy, a free camp that combined learning with water sports, martial arts, technology and dance programs in the afternoon.

Among the new activities that Summer Dreamers will offer this year is “positive spin,” in which middle school students will build bicycles and ride city trails, culminating in a bike tour along the Youghiogheny River Trail and an overnight camping trip.

Along with getting leery parents and students on board for summer school, Augustine said some school superintendents remain uncertain of the value of summer classes, especially now that they face daunting financial challenges.

“This is not a time when districts have the money lying around to start these programs,” Augustine said. “But summer school costs should not fall on school systems alone.”

She cited 100 federal sources that schools can tap, including Health and Human Services and Child Care and Development Fund dollars.

Using outside funding can deflect criticism from middle-class parents who don’t understand funding summer kayaking opportunities for struggling students while cutting arts and music for all children.