By CHESTER E. FINN JR.

"He who labors diligently need never despair, for all things are accomplished by diligence and labor." —Menander

How many days a year did the future Alexander the Great study with Aristotle? Did Socrates teach Plato on Saturdays as well as weekdays? During summer's heat and winter's chill?

Though such details remain shrouded in mystery, historians have unearthed some information about education in ancient times. Spartans famously put their children through a rigorous public education system, although the focus was on military training rather than reading and writing. Students in Mesopotamia attended their schools from sunrise to sunset.

In the face of budget shortfalls, school districts in many parts of the United States today are moving toward four-day weeks. This is despite evidence that longer school weeks and years can improve academic performance. Schoolchildren in China attend school 41 days a year more than most young Americans—and receive 30% more hours of instruction. Schools in Singapore operate 40 weeks a year. Saturday classes are the norm in Korea and other Asian countries—and Japanese authorities are having second thoughts about their 1998 decision to cease Saturday-morning instruction. This additional time spent learning is one big reason that youngsters from many Asian nations routinely out-score their American counterparts on international tests of science and math.

"Summer learning loss" is no joke. When they return to school in late August or early September, many children, especially the least advantaged among them, have shed a sizable portion of what they had learned by May—a full month's worth, by most estimates, adding up to 1.3 school years by the end of high school.

The typical young American, upon turning 18, will have spent just 9% of his or her hours on this planet under the school roof (and that assumes full-day kindergarten and perfect attendance) versus 91% spent elsewhere. As for the rest of that time, the Kaiser Family Foundation recently reported that American youngsters now devote an astounding 7.5 hours per day to "using entertainment media" (including TV, Internet, cellphones and videogames). That translates to about 53 hours a week—versus 30 hours in school.

It's scarcely news that young Americans devote less time to formal learning than their international counterparts. A federal commission on time and learning reported 16 years ago that "students in other postindustrial countries receive twice as much instruction in core academic areas during high school." Required courses in those four years consumed 3,280 hours in French schools versus 1,460 in the U.S. Young Germans routinely devoted two hours a night to homework. Half of Japan's ninth graders moved every afternoon from school to private "juku" for additional instruction in core subjects.

Nor is it news that "time on task" has a powerful influence on educational attainment. In 1994, for example, economist Robert Margo reported that historical differences in school-year length for black and white youngsters attending segregated schools accounted for much of the gap in their adult earnings.

A fascinating new study by University of Maryland analyst Dave Marcotte shows that even the loss of a few instructional days can erode academic performance. Examining the days forfeited to snow and other "unscheduled closings" in Maryland in 2002-2003, he concluded that two-thirds of the elementary schools that failed to make "adequate yearly progress" (the federal benchmark under "No Child Left Behind") in math that year would have done so "if they had been open during all scheduled school days."

Where things start to get complicated is that time spent in school does not equal time fruitfully applied to learning basic skills and core content—a mismatch that looms larger in the U.S. than in most other places. Measured by simple clock hours or days per year in school, we look good alongside Europe and decent in comparison with most of Asia. Not good enough, especially for disadvantaged kids whose nonschool hours often undermine what they're taught in class, but pretty good.

Our deeper problem is the enormous amount of time that typical American schools spend on gym, recess, lunch, assembly, changing classes, homeroom, lining up to go to the art room, looking at movies, writing down homework assignments, quieting the classroom, celebrating this or that holiday, and other pursuits. It's not all wasted time but neither are these minutes spent in ways that boost test scores, enhance college-readiness or deepen pupils' understanding of literature, geography or algebra.

Visit a KIPP school or another high-performance institution and you find that a big reason for the longer day is that it accommodates these nonacademic pursuits without sacrificing the instructional core. They tolerate remarkably little wasted time, particularly in the classroom setting. Their teachers squander minimal class time on discipline challenges or distributing and collecting materials. They systematically deliver lessons that are carefully planned and structured—and youngsters who need additional help to understand something get it later, sometimes in the evening via the teacher's cellphone, so that the entire class doesn't need to pause for an explanation.

Longer school days and years also aid working parents; for many of them, 2:30 dismissal times and three-month summer breaks are more burden than benefit. And the more time kids spend in safe schools, the less time they have to go astray at home or in the neighborhood.

Critics of extending the day and year occasionally note, with some justification, that U.S. schools don't need more total time so much as they need to make better use of the time they've got. Indeed, the 1994 "time and learning" commission underscored that point in its recommendations, which urged schools to set aside a full 5.5 hours every day for "core subjects"—nearly doubling the time devoted to them.

Yet American public education is so hard to change in fundamental ways—so much like turning an aircraft carrier or, as Admiral Hyman Rickover once remarked, moving a cemetery—that reform typically comes by adding something on top of what we already have. It's actually easier to add an hour to the school day or a few weeks to the year than to alter the established routines of schools and school systems. (A worthy nonprofit outfit called the National Center on Time and Learning is working at such additions—and can point to some success in its pilot schools in Massachusetts.)

As with everything else in public education, however, the threat of change brings interest groups out of the woodwork. Although many parents—particularly poor and working-class parents—welcome the prospect of schools tending to a larger portion of their kids' lives, others are so enamored of their summer cottages, travel plans, grandparent visits, after-school piano lessons and soccer leagues that they balk at any big shifts in calendar or schedule.

Communities that have experimented with "year-round" schooling have often had to backtrack under pressure from the summer-vacation industry, including camps needing counselors, resorts needing waiters, pools needing lifeguards—and all of them needing clients with "traditional" vacation schedules. After 13 years, Jefferson County, Colo., abandoned its year-round school calendar in 1989. The longer school year lasted nine years in Prince William County, Va.

This issue brings out the teacher unions, too, demanding more pay for extra hours, hence fatter school-system budgets in a lean fiscal time. Little wonder that taxpayers are legitimately wary. It's no secret that public education's institutional imperatives point toward more of everything, especially money. School systems are keen to mount programs for 4-year-olds, for instance, and (so long as they get the cash from local, state, federal or philanthropic sources) to run summer schools and extended-day programs, up to and including three meals a day for participants. Some of this is absolutely legitimate—an earnest effort to respond to the needs of children and families in their communities and to the academic-results-based accountability regimens of state and national governments. But some of it reflects the inexorable expansionism and unquenchable appetites of the public sector and its employees.

Over the long run, technology holds much potential to boost student learning time in flexible ways and at modest cost. We can stipulate that kids are addicted to it; that "virtual" instruction can happen at very nearly any time or place; and that well-designed distance-learning programs (and suitable hardware) enable greater individualization of learning, with each child moving at his/her own pace, diving deeper when warranted, and going back over things they didn't quite understand the first time. This already happens in the best online schools, of which the U.S. already has several dozen, often operating statewide, such as the Florida Virtual School and Ohio Virtual Academy.

It also happens in "hybrids" that make astute and economical use of computer-delivered instruction, testing and such within brick-and-mortar schools that also have flesh-and-blood teachers. Rocketship Education, a small but growing network of elementary charter schools in San Jose, Calif., is such a creation, skillfully blending online lessons, practice and testing with a small but terrific team of instructors.

With continuing advances in hardware and software, the boundaries among "learning in school," "learning in other settings" and "learning on your own" will gradually disappear, with potent implications for time spent learning, which need no longer be confined to the classroom hours stipulated in the teachers' union (or custodians' union) contract or the 180-day year prescribed in state law (and, in some jurisdictions, not allowed to start before Labor Day).

But we must not be naive. The education establishment will vigorously defend those traditional boundaries and "gradually" may be a long time in coming. Just as important, although most youngsters are self-motivated when it comes to what Kaiser terms "entertainment media," far fewer will take the initiative to learn more geometry or rules of grammar on their own. While glitzy technology will make such things more tempting for more kids, and well-organized (and prosperous) parents can help make that happen, millions of girls and boys are likely to continue doing most of their academic learning in places called school, during "school hours" and under a teacher's supervision.

Which brings us back to high-performance schools, institutions that commandeer far more than 9% of their students' lives and use the extra time to accomplish three things: more hours to imbibe important skills and knowledge; fewer hours outside school to waste or get into trouble; and a de facto culture transplant, wrought by dynamic teachers who instill in their young charges the college aspirations, appreciation of learning, good behavior and orderly habits that are too often missing from homes and neighborhoods.

Disadvantaged youngsters really need—for their own good—the benefits of longer days, summer classes and Saturday mornings in school. But nearly every young American needs to learn more than most are learning today, both for the sake of their own prospects and on behalf of the nation's competitiveness in a shrinking, dog-eat-dog world. Yes, it will disrupt everything from school-bus schedules to family vacations. Yes, it will carry some costs, at least until we eke offsetting savings from the technology-in-education revolution. But even Aristotle might conclude that this is a price worth paying.