But these initiatives - favored by President Obama and floated in recent months by officials in the District, Prince George's County and Alexandria - have run into more immediate political realities. Budgets are tight. Rules are restrictive. And some parents have balked at locking more of their children's lives into structured activities.
The fight brewing in Alexandria has some of these elements. Superintendent Morton Sherman has proposed extending the calendar by starting classes a week before Labor Day. That idea had been up for a School Board vote Thursday night but was abruptly postponed, according to a statement on the school system Web site, to allow time for board deliberation and community consultations. Sherman also favors a longer school day, which might come to a vote later in the year.
"My position is really straightforward," Sherman said. "First, quality teachers matter in kids' lives. Second, time matters. Whether it's 10 minutes or 300 hours, time spent with a quality teacher makes a difference. That's irrefutable."
But many parents, teachers and students complained about his proposals at a School Board meeting last week. Even if the board approves the earlier start date for classes, state officials would have to approve it under a Virginia law that calls for summer vacation to last until after Labor Day.
"The kids are already hitting that saturation point," said Cindy Anderson, whose son is a senior at T.C. Williams High School. "Even if they're struggling, more time in the classroom might not be the solution."
The typical school day is about 61/2 hours. Some well-regarded charter schools, such as those run by the Knowledge Is Power Program, have had success improving student performance with longer days as well as mandatory weekend or summer sessions.
Initiatives to extend learning time have been particularly common in districts with high poverty rates and high percentages of minority students. The Center for American Progress, a liberal think tank, found that there were more than 300 such initiatives in 30 states between 1991 and 2007.
Under Obama, the idea has gained even more momentum in some reform circles. His administration has argued that more time in class is essential to helping the United States compete with countries such as South Korea that have higher international test scores.
The research, however, is inconclusive. Harris Cooper, a psychology professor at Duke University who has studied school calendars, said the most important issue is how the hours are spent.
"Additional time can have an positive impact," Cooper said. "But the added time has to be significant enough to change the way instruction is delivered. That's the collective wisdom of those who have studied the issue."
Advocates contend that expanding the school day would allow teachers to devote more time to art, music, social studies, physical education and science. Many schools have cut back in those subjects in recent years as they have concentrated on reading and math, which are the focus of most standardized tests.
"The bottom line is that the length of the school day is no longer realistic when you consider the amount of content kids are expected to learn today compared to 30 years ago," said Jennifer Davis, president of the National Center on Time & Learning, based in Boston. "Across the country, we're hearing that teachers don't feel like they have time to cover the curriculum or meet the needs of individual students during the length of the school day."
In late November, a few days before he took office as Prince George's County executive, Rushern L. Baker III (D) endorsed longer days to improve elementary and middle schools. But Prince George's Schools Superintendent William R. Hite Jr. said he is not able to pursue that proposal this year because of budget shortages.
In October, D.C. Council member Mary M. Cheh (D-Ward 3) proposed lengthening the city's school day by a half-hour. Her bill died at the end of the year, aides said, but Cheh is still exploring how to give students more class time.
In Alexandria, Sherman said more class time is essential for a 12,000-student system, which for years has fallen short of academic targets. The city serves a population less affluent than that of some neighboring suburbs, which means that its students have more educational challenges.
Under Sherman's plan, the Alexandria school year would grow by two days, to 185. Schools are in session 182 to 184 days in Arlington County and 183 in Fairfax County. D.C. public schools are open 180 days. The Montgomery County school year is 184 days.
In a separate proposal, Sherman wants to extend the school day by 30 minutes, to more than seven hours. Whether the proposals will advance is unclear. If both proposals were approved, they would add $2 million to a proposed budget of about $210 million.
Emma Schutzius, an eighth-grader at George Washington Middle School, said educators should focus on keeping kids interested in learning. "We are not just walking, talking test scores," she said.
Staff writers Christy Goodman and Kevin Sieff contributed to this report.