The general assumption is that when it comes to educating American kids, more is more. Longer school hours. Saturday school. Summer school. Yet more than 120 school districts across the nation are finding that less can also be more — less being fewer days spent in school.

The four-day school week has been around for decades, according to the National Council of State Legislatures, but it’s quietly spreading as a money-saving tactic, especially after several states — including Montana, Georgia, Missouri and Washington — passed legislation allowing school districts to make the switch as long as they lengthened each school day so that there was no reduction in instructional hours. Teachers work just as much under the four-day plan, so there are no cost reductions there, but schools have saved from 2 percent to 9 percent, according to a 2009 report by the Center for Education Policy at the University of Southern Maine. Utility and transportation costs are lower; there’s no need to serve a fifth lunch each week; even the reduced wear and tear on buildings has helped.

Here’s the surprise: There appear to be educational benefits as well. Absenteeism among students and teachers in these schools has fallen appreciably, the report said. (As a result, schools also paid less money for substitute teachers.) Students reported feeling more positive about school. Dropout rates fell, students behaved better and participation in extracurricular activities rose. Parents of young children often objected to the change because of the need to find child care, but once the programs were in place, the report said, they often found that it was easier to find care for one full day a week than for several partial days. Test scores didn’t fall, and in many cases, they rose.

As promising as all this sounds, the findings are far from definitive. The four-day week has been tried mostly in tiny, rural school districts. Providing the necessary child care could be more of a challenge in urban areas. And despite the findings above, four-day schedules might turn out to be more helpful to high school students than children in primary grades, who have shorter attention spans. For those children, teachers said, it would help to schedule meatier academic subjects early in the day, but it still means the later hours are likely to be less academically productive.

Four-day school weeks aren’t an educational panacea, but they are intriguing.