U.S. Education Secretary Arne Duncan wants Philadelphia's schoolchildren - and those around the country - to have longer school days and shorter summer breaks.

"Six hours a day just doesn't cut it," said Duncan, who comes to town tomorrow to tour two city schools and meet with local education officials. "Our school calendar's based on a 19th century agrarian economy. I'm sure there weren't too many kids in Philadelphia working in their parents' fields this summer."

The message is in keeping with one given this year by President Obama, who told reporters that in order to remain competitive, U.S. children should spend more time in school.

"We're desperately short on time," Duncan said today. "Children in India and China are going to school much more than our students are."

Former House Speaker Newt Gingrich, Rev. Al Sharpton and Duncan will visit one of the four Mastery Charter School campuses and McDaniel Elementary, a public school, on their first stop of a multicity tour. Sharpton and Gingrich - strange bedfellows from on opposite sides of the political spectrum - agreed to the tour after a White House visit this spring, where Obama suggested the three together could draw attention to the need for wholesale change in American schools.

Though all three agree that American education must be remade, in interviews the trio already showed that they sharply disagree on some points.

Gingrich said that "Philadelphia has some very bad public schools - traditional schools, I call them, bureaucratic schools. And it has some very good charter schools."

Duncan's take on the city's public schools?

"You have great leadership there, a great superintendent, folks that are willing to change the status quo," said Duncan.

Philadelphia schools Chief Arlene Ackerman, he said, "is one of the best superintendents in the country. She's got a laserlike focus on closing the gap and raising the bar." Though she's only been on the job a little over a year, Duncan said, he likes her ideas for reform and her willingness to shake things up.

In academics, Philadelphia schools have made much progress and have much further to go, Duncan added.

Of the state of public education in Philadelphia and elsewhere, Sharpton said: "It's like there's a crack in the Liberty Bell. There's a crack in education." Sharpton called education the civil right of the 21st century.

In Philadelphia, for instance, about half of all students cannot read or do math on grade level. The dropout rate hovers around 50 percent as well.

Equal funding, strong teachers at all schools, and parent participation are the keys to turning the system around, Sharpton said. He also called for more accountability for teachers and administrators.

The civil rights activist said he believes that means merit pay for teachers, giving higher salaries to those who help students improve their test scores. It's a message most teachers' unions - including Philadelphia's, where the issue is on the table in the current contract negotiations - reject.

"I'm pro-union, I'm not for union-busting, but even unions know that they're going to have to adjust," said Sharpton. "We cannot just sit by and allow education to continue the way it's been going."

Unlike public schools - where a typical school day is about seven hours, with time subtracted for lunch - charter schools have the freedom to have longer school days, as Duncan has called for.

At Mastery, for instance, the instructional day is eight hours long, and students are required to spend even more time in class or go to school on Saturdays if they're behind on work.

Gingrich, who champions an national expansion of charters, wants stronger charter laws in all 50 states. He dismissed the notion that charter schools need tighter controls, even as federal authorities conduct investigations into possible financial mismanagement at at least six Philadelphia-area charters. There are 67 charter schools in Philadelphia.

"There are an amazing number of bureaucratic systems that have had even deeper problems of misuse of money, failure to educate students," said Gingrich. "That's . . . a waste of taxpayer money, but much more tragically, a waste of the students' lives."

Still, he said, charters must be transparent, and the charter selection process must be thorough.

"This is not 'write a check to every entrepreneur who shows up,' " said the former House speaker.

Duncan said he supports Ackerman's plan to shut up to 35 failing public schools in the next five years and reopen them as charters or schools run by outside managers or other individuals.

He presided over a similar initiative in Chicago, where he was schools chief until this year. Critics here say they don't want to give away public schools.

"What we have to give up on is academic failure," Duncan said. "What you have are dropout factories - you have places that for the overwhelming majority of students are simply not doing them justice. To perpetuate something that has chronically underperformed, how can we be wedded to that?"

Look at Mastery Charter-Shoemaker campus, a former public school that was successfully transformed into a charter school, Duncan said. Its scores have risen dramatically since the transformation - between 2006 and 2009, the percentage of eighth graders who passed state reading tests jumped by about 40 percent, to over 80 percent proficient; and in math, the percentage was up by more than 50 percent, to about 85 percent passing.

"Nobody can say any more, these kids can't learn. It puts the lie, the myth, the stereotype that poor children and minority children can't learn to rest. Students from very tough backgrounds are performing extra-well at Mastery."

Contact staff writer Kristen Graham at 215-854-5146 or kgraham@phillynews.com.