For many Washington area kids, summer is a footloose season marked by family trips and shuttling from camp to camp. But for poor children, the hot months are often filled with empty time that stultifies learning.

The opportunity gap has widened this year as some cash-strapped local agencies have eliminated thousands of summer school slots, leaving needy students with fewer ways to keep pace with their more affluent peers.

Battling the summer slide in the District is Horizons Greater Washington, one of a handful of privately funded efforts that seek to turn summer into an advantage — instead of a liability — for children from low-income families.

For six weeks each June and July, 130 children, most from the public H.D. Cooke Elementary School, are bused to the private Maret School in Woodley Park, where spots on campus offer a view of the spires of the Washington National Cathedral peeking over a green canopy of trees.

Students spend part of each day puzzling over math problems and studying vocabulary. But they also dive into hands-on, beyond-the-basics science activities, such as building lava lamps, making toothpaste from scratch and programming robots to navigate obstacle courses. And they get a dose of summer-camp staples, from white-water rafting to arts and crafts.

“They’re hungry to learn,” said Kiki Sweigart, a fifth-grade teacher at Maret who has directed the program here since its founding in 2000. “What we want them to know is that there is a big world out there, a lot of doors open for you, but you have to want it, you have to work for it.”

The program is well regarded for substantially boosting students’ reading skills. But that’s not why many students, recruited in kindergarten, agree to return year after year.

“I keep coming back because it’s a really fun place to go,” said Ashley Vigil, 12, a six-year Horizons veteran, who was gabbing with friends one morning this month before math class.

“Pizza,” added Frankie Borges, 7. “And we go swimming!”

Daily swimming lessons at the Swiss Embassy pool, which is next door to Maret, are a key part of the program. Teachers say children develop confidence, and learn the value of patience and practice, while progressing from shallow to deep water and from the dog paddle to a respectable crawl.

“If you can teach a kid to go swimming, they think they can do anything,” said Mario Alas, 15, who spent nine years as a Horizons student before he became a counselor this summer.

He recalled arriving as a kindergartner, terrified of the pool. Now he is a rising 10th-grader at Duke Ellington School of the Arts who plays guitar and piano and aims to earn three university degrees, in law, music and engineering.

Model for reform

Programs such as Horizons offer a summer model for education reform, said Matthew Boulay, the interim chief executive of the Baltimore-based National Summer Learning Association. But he said school systems and communities must help foot the bill.

“There’s a real disconnect between how much we know about the negative impact of summer learning loss and what is actually being done in terms of policy and programming,” he said. “We spend nine months, from September through May or June, devoting enormous amounts of time and energy — not to mention resources — to promoting student achievement and learning. And then we step away for three months and allow a good portion of those gains to be lost.”

Nearly all children forget some of what they know over the summer. But researchers have discovered that poor children tend to forget more — so much more that by ninth grade, according to a 2007 study, two-thirds of the achievement gap between children from low-income and middle-class families can be explained by what happens during summer.

Demand outpaces supply

Nonetheless, school systems faced with shrinking budgets have curtailed summer offerings.

D.C. public schools offered about 5,100 summer school slots this year — down more than half from the enrollment of 10,720 last year. Prince George’s County schools have summer slots for 2,250 children, less than 2 percent of those enrolled in the county’s public schools.

Fairfax County has cut summer school funding from $22.6 million in 2007 to $8.9 million this year, according to county summer school director Levi Folly. Fairfax once offered about 4,000 summer school slots at the elementary level and the same number at the middle school level, he said, but now there almost none.

Similar cuts have occurred across the country in cities such as Los Angeles, Philadelphia and Seattle.

The national network of Horizons programs, meanwhile, has managed to grow.

Founded in 1964 at a private school in Connecticut, Horizons National began expanding in the 1990s and now operates at 20 sites in 10 cities as far west as Denver.

In the Washington area, the program recently added two sites. In 2009, St. Patrick’s Episcopal Day School in the Palisades began hosting students from the District’s public Bancroft Elementary School in Mount Pleasant. Last year, the private Norwood School in Bethesda opened its doors to students from Montgomery County’s public Rock Creek Forest Elementary School.

Host schools offer free classroom space and other in-kind resources, and private donors provide funding.

In the past two years, the Wallace and Bill and Melinda Gates foundations, among others, have poured millions of dollars into identifying, studying and replicating successful summer programs for needy students.

The Wal-Mart Foundation last month announced a grant of $11.5 million spread among summer learning programs in 10 cities. A recipient in the District was Higher Achievement, a four-year program for middle school students. The grant helped offset shrinking government support.

“We’d like to be able to invest in things that are going to work, obviously, and the return on investment on this I think is very high,” said Wal-Mart Foundation President Margaret McKenna.

Private funding cannot entirely make up for lower public spending, however. Reliable national data on student summer activities are difficult to come by, but demand for educational programs outpaces supply.

Nicolasa Vigil, mother of 12-year-old Ashley, said she is grateful that her daughter is one of the lucky few who found their way to Horizons. She called the program, which costs her just $25 a year, a “blessing.”

“There are a limited number of summer camps, but they’re so expensive that I don’t think we would be able to afford them,” she said. “That’s just the reality.”