Former Secretary of State Hillary Rodham Clinton addresses around 3,000 summer camp and out of school time professionals at the American Camp Association and Tri State CAMP conference Thursday. (AP Photo/Mel Evans)

What many observers say will be Hillary Rodham Clinton's final paid speech before she begins a presidential campaign was addressed to the American Camp Association. Everyone loves summer camp, and the former secretary of state didn't talk about anything controversial.

"We have a huge fun deficit in America, and we need to figure out how to fill that fun deficit," she said, suggesting summer camps for adults (presumably in jest) .

Summer camp isn't only about fun, though. Summer camp--along with academic year extracurriculars--are an important way that kids learn to get along with their peers, have fun -- and keep their young brains active outside of school. That is, for those of them whose parents can afford it.

With her remarks, Clinton had an opportunity to talk about the real fun deficit in America, the fun deficit for children in poor families. It wouldn't be surprising, given her past, if she focuses on this issue more squarely in a campaign.

Recent work has shown that this gap in fun extends throughout the school year. Robert Putnam, the sociologist who just released a widely discussed book on poverty in childhood, has found that children in the upper middle class have become more involved in sports and clubs at school over the past forty years. Working-class students have become much less so, according to survey data. Football practice is less and less the kind of place where kids can form close friendships with people from other social classes.

Putnam is particularly concerned about schools charging students fees in order to participate. While some districts might waive these fees for poor students, Putnam argues that parents who aren't well off might not understand how to apply for a waiver and might feel that doing so carries some kind of stigma. And even where waivers are available, many sports teams and other clubs are private organizations that are not formally associated with school district and require hefty participation fees.

The winners in this game aren't just the ones who have the most fun. As Putnam has argued at length, our relationships with our neighbors have an important effect on our ability to withstand an illness or a bad economy or to get ahead in the world. Extracurriculars create and reinforce those bonds -- whether between a student from an immigrant family and her debate coach, or between a lawyer and a waitress watching their children's soccer game together on a Saturday morning.

The same kinds of questions can come up over summer breaks. Researchers have long understood that students forget some of what they've learned during the previous school year over the summer -- typically, about a month of instruction. Kids never quite make up what they've forgotten, and over the 12 glorious summer vacations before a child graduates high school, these losses add up. Poor children tend to forget much more, and the fact that their parents can't pay for them attend to various summer activities is probably part of the reason. As Bridget Ansel recently noted in Politico:

Research shows that any high-quality summer program that keeps children engaged — whether that is a traditional camp, summer school or even frequent trips to the museum — can mitigate summer learning loss.

The problem is, not everyone can afford to send their kids to a fancy summer program. That means low-income children (exactly the children that could benefit most from such programs) cannot afford to participate. Meanwhile, in a world in which most children grow up in a household without a full-time caregiver, low-income parents not only struggle to find full-time care but also must divert large a large fraction of their limited salaries to pay for it.

It's an argument that Clinton understands well. Putnam has said that a book she published in 1996, It Takes a Village, anticipated some of his ideas. And when she turns to the presidential campaign, she may well turn to those issues.

Emily Badger contributed to this report.