Did your kids moan that winter break was way too short as you got them ready for the first day back in school? They might get their wish of more holiday time off under proposals catching on around the country to lengthen the school year.

But there’s a catch: a much shorter summer vacation.

Education Secretary Arne Duncan, a chief proponent of the longer school year, says American students have fallen behind the world academically.

“Whether educators have more time to enrich instruction or students have more time to learn how to play an instrument and write computer code, adding meaningful in-school hours is a critical investment that better prepares children to be successful in the 21st century,” he said in December when five states announced they would add at least 300 hours to the academic calendar in some schools beginning this year.

The three-year pilot project will affect about 20,000 students in 40 schools in Colorado, Connecticut, Massachusetts, New York and Tennessee.

Proponents argue that too much knowledge is lost while American kids wile away the summer months apart from their lessons. The National Summer Learning Association cites decades of research that shows students’ test scores are higher in the same subjects at the beginning of the summer than at the end.

“The research is very clear about that,” said Charles Ballinger, executive director emeritus of the National Association for Year-Round School in San Diego. “The only ones who don’t lose are the upper 10 to 15 percent of the student body. Those tend to be gifted, college-bound, they’re natural learners who will learn wherever they are.”

Supporters also say a longer school year would give poor children more access to school-provided healthy meals.

Yet the movement has plenty of detractors — so many that Ballinger sometimes feels like the Grinch trying to steal Christmas.

“I had a parent at one meeting say, ‘I want my child to lie on his back in the grass watching the clouds in the sky during the day and the moon and stars at night,”’ Ballinger recalled. “I thought, ‘Oh, my. Most kids do that for two, three, maybe four days, then say, `What’s next?””

But opponents aren’t simply dreamy romantics.

Besides the outdoor opportunities for pent up youngsters, they say families already are beholden to the school calendar for three seasons out of four. Summer breaks, they say, are needed to provide an academic respite for students’ overwrought minds, and to provide time with family and the flexibility to travel and study favorite subjects in more depth. They note that advocates of year-round school cannot point to any evidence that it brings appreciable academic benefits.

“I do believe that if children have not mastered a subject that, within a week, personally, I see a slide in my own child,” said Tina Bruno, executive director of the Coalition for a Traditional School Calendar. “That’s where the idea of parental involvement and parental responsibility in education comes in, because our children cannot and should not be in school seven days a week, 365 days a year.”

Bruno is part of a “Save Our Summers” alliance of parents, grandparents, educational professionals and some summer-time recreation providers fighting year-round school. Local chapters carry names such as Georgians Need Summers, Texans for a Traditional School Year and Save Alabama Summers.

Camps, hotel operators and other summer-specific industries raise red flags about the potential economic effect.

School days shorter than work days and summer breaks that extend to as many as 12 weeks in some areas run up against increasing political pressure from working households — 30 percent of which are headed by women.

These families must fill the gaps with afterschool programs, day care, babysitters and camps.

“Particularly where there are single parents or where both parents are working, they prefer to provide care for three weeks at a time rather than three months at a time,” Ballinger said.

The National Center on Time & Learning has estimated that about 1,000 districts have adopted longer school days or years.

Some places that have tried the year-round calendar, including Salt Lake City, Las Vegas and parts of California, have returned to the traditional approach. Strapped budgets and parental dissatisfaction were among reasons.

At the heart of the debate is nothing less than the ability of America’s workforce to compete globally. The U.S. remains in the top dozen or so countries in all tested subjects.

But even where U.S. student scores have improved, many other nations have improved much faster, leaving American students far behind peers in Asia and Europe.

Still, data are far from clear that more hours behind a desk can help.

A Center for Public Education review found that students in India and China — countries Duncan has pointed to as giving children more classroom time than the U.S. — don’t actually spend more time in school than American children, when disparate data are converted to apples-to-apples comparisons.

The center found 42 U.S. states require more than 800 instructional hours a year for their youngest students, and that’s more than India does.