Every fall, students across the nation welcome a new school year with new teachers, new books, new supplies — and old lessons. Re-teaching material from the previous school year has become part of the back-to-school tradition, but it is a costly one that acknowledges the underlying risks of a summer devoid of learning.

Research shows that most children lose approximately two months of grade-level equivalency in math skills when they are out of school over the summer. For students from low-income families, the loss of skills is even more pronounced in reading. While higher-income peers maintain their skills or even make gains, low-income children fall behind by more than two months of reading skills.

The cumulative effects of falling behind summer after summer widen the achievement gap and lead to higher high school dropout rates. One Johns Hopkins study found that summer learning loss is responsible for as much as two-thirds of the disparity in reading achievement between lower-income and higher-income children by the ninth grade. With the new Common Core State Standards setting the bar even higher for academic performance and college readiness, summers without learning are likely to put low-income students even further behind and to keep many students from reaching these new targets.

However, recent research from the RAND Corp. also shows that quality summer programs can make a significant difference in stopping the harmful effects of the “summer slide.” As some school districts are recognizing, children who spend five or six weeks of their summer break in programs that provide academic rigor and engaging activities can experience gains in skills rather than losses.

They also benefit from physical activity and healthy meals often provided in these programs. In cities such as Houston, Pittsburgh and Baltimore, school district leaders have begun to move away from the remedial model of summer school and embrace a new vision of summer learning that is both attractive to their students and an essential component of their education reform agendas.

At Horizons programs across the country, more than 2,000 low-income public school students spent their summer on a private school or college campus, receiving academic instruction from committed teachers, participating in enriching trips to cultural institutions and learning to swim. In 2011, students gained an average of two to three months in math and reading skills by the end of the six-week program.

And at the United Way of Santa Barbara County, 250 youth ages 7 to 18 — all of whom are from low-income families — spent this past summer reading, writing, participating in service learning projects, taking field trips and receiving healthful meals. Parents of participating students also were offered weekly parent education workshops.

In 2011, 82 percent of participants in the program jumped 2.1 grade levels in reading comprehension, phonics and vocabulary skills, according to tests administered at the start and end of the summer. Instead of falling behind and needing to catch up, these youth moved ahead and started the school year ready for new learning challenges.

The results of effective summer programs like these can be striking — especially for youth who are most vulnerable to summer learning loss. Yet too few school systems and communities are recognizing the potential for summer learning experiences to provide a boost to education reform efforts.

No matter which political party wins in the coming presidential and congressional elections, our schools will continue to face tough budget choices. That makes it more important than ever for school leaders and community partners to move forward with promising strategies that will help make the most of the taxpayer investments in education for years to come. It’s time to wake up and acknowledge what teachers see firsthand each fall as they revisit old lessons: the current school calendar significantly undervalues the summer.

When more of our school leaders recognize the consequences of summer learning loss and the payoff of supporting high-quality summer learning experiences, we will all reap the benefits of developing our next generation of leaders and workers. And when more youth have the opportunities they need to make the most of their summer, we will be able to transform the back-to-school season to what it should be — a time marked by fresh skills, fresh lessons and a fresh outlook on achieving student success.

• Huggins is CEO of the National Summer Learning Association.