Many millions of dollars have been spent this year on experiments with teacher evaluation systems, standardized tests and the expansion of charter schools. But when it comes to finding the resources to keep schools open five days a week and classes at a reasonable size, well, not so much.

Four-day school weeks in a small but growing number of school districts are a result of the economic crisis around the country, according to this story by my colleague Lyndsey Layton. More than 290 school districts — up from an estimated 120 two years ago — now have four-day weeks with extended hours to make up for the lost day.

Though that is a mere fraction of the 15,000 districts in the country, it reveals the extremes some school systems feel they must go to to deal with their financial woes. Other bad remedies include expanding class size to 40, 45, 50 or even more students, cutting afterschool programs, etc.

Four-day school weeks — which generally absorb the same number of classroom hours as five-day weeks — are not new. Some rural districts have operated in this manner for a number of years, and many of them like it — and not only because it saves money on transportation and other costs.

They say the long days allow for deeper lessons (though bloc scheduling five days a week can achieve the same in-depth lesson periods), and absenteeism among students and teachers has declined in some four-day-a-week districts.

Other districts that have experimented with four days didn’t like it and went back to five. Some teachers worry that three-day weekends can make it harder for kids to retain what they learned at school, and others say that teaching and learning inevitably suffer. Younger students are likely to have trouble sitting in longer classes and staying focused (which is why some four-day-a-week schools don’t focus on academics, which could mean these students wind up getting fewer lessons). Working parents have to make child care arrangements for the day when their kids used to be at school but no longer are.

The bottom line is that there is no conclusive research on how students are educationally affected by spending four days at school rather than five — though with the same amount of hours.

In fact, there is no conclusive evidence on exactly how much time all kids need to spend in class to be successful. How much a student learns each day is dependent on a number of sometimes changing in-school and out-of-school factors.

If teachers are forced into four-day weeks without time to learn how to develop new lessons that fit the new time frame, the learning process is bound to suffer, and kids can sit in class for hours on end with little benefit. If kids come to school unprepared to learn — tired, or sick, or angry, or stoned — the number of class hours isn’t going to matter much.

However, if kids come to school ready to learn, and teachers know how to develop lessons that capture the students’ interests and engage them in a focused way, four days a week may result in no educational deficit. Five days isn’t sacrosanct.

The irony in all of this is that the education reform movement is big on “seat time,” with charter schools such as KIPP frequently touted for keeping kids in class far longer than traditional schools.

Rising test scores at these schools are commonly linked to the greater amount of seat time, though there surely are other factors at KIPP that go into that as well. For example, I recently asked KIPP co-founder Mike Feinberg whether a KIPP school would help a student get glasses if he or she needed them, and he said yes. That kind of assistance surely would have an effect on how well a student does.

Some public schools have class six days a week, and others are considering expanding. Baltimore’s public school officials have been considering a proposal for a six-day school week. Saturday school has helped some kids and hasn’t helped other kids.

There isn’t one prescription that works for every school or community of kids — even if school reformers insist there is.

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