Earlier this month, J.C. Penney learned the hard way just how powerful the home-schooling movement has become. Penney's had recently started selling a T shirt that wickedly crystallized many people's assumptions about the movement: home skooled, giggles the shirt, which also depicts a trailer home. The folks at Penney's say they meant no harm — they didn't even design the T, which had become popular in other stores first. But they yanked it from the shelves Aug. 8 after enraged missives poured in from home-schooling families, some of whom threatened a boycott.

Penney's should have known better. Over the past decade, the ranks of families home schooling have grown dramatically. According to a new federal report, at least 850,000 students were learning at home in 1999, the most recent year studied; some experts believe the figure is actually twice that. As recently as 1994, the government estimated the number at just 345,000. True, even the largest estimates still put the home schooled at only 4% of the total K-12 population — but that would mean more kids learn at home than attend all the public schools in Alaska, Delaware, Hawaii, Montana, New Hampshire, North Dakota, Rhode Island, South Dakota, Vermont and Wyoming combined.

While politicians from Washington on down to your school board have been warring over charter schools and vouchers in recent years, home schooling has quietly outpaced both of those more attention-getting reforms (only half a million kids are in charter schools, and just 65,000 receive vouchers). In many ways, in fact, home schooling has become a threat to the very notion of public education. In some school districts, so many parents are pulling their children out to teach them at home that the districts are bleeding millions of dollars in per-pupil funding. Aside from money, the drain of families is eroding something more precious: public confidence in the schools.

Thomas Jefferson and the other early American crusaders for public education believed the schools would help sustain democracy by bringing everyone together to share values and learn a common history. In the little red brick schoolhouse, we would pursue both "democracy in education and education in democracy," as Stanford historian David Tyack gracefully puts it. Home schooling forsakes all that by defining education not as the pursuit of an entire community but as the work of one family and its chosen circle. Which can be great. Despite some drawbacks, there are signs that home-schooling parents are doing a better job than public schools at teaching their kids. But as the number of kids learning at home grows, we should pause to wonder: Better at teaching them what? Home schooling may turn out better students, but does it create better citizens?

To see how home schooling threatens public schools, look at Maricopa County, Ariz. The county has approximately 7,000 home-schooled students. That's only 1.4% of school-age kids, but it means $35 million less for the county in per-pupil funding. The state of Florida has 41,128 children (1.7%) learning at home this year, up from 10,039 in the 1991-92 school year; those kids represent a loss of nearly $130 million from school budgets in that state. Of course the schools have fewer children to teach, so it makes sense that they wouldn't get as much money, but the districts lose much more than cash. "Home schooling is a social threat to public education," says Chris Lubienski, who teaches at Iowa State University's college of education. "It is taking some of the most affluent and articulate parents out of the system. These are the parents who know how to get things done with administrators."

To be sure, many public schools — and their baleful unions and wretched bureaucrats, their rigid rules and we-know-best manner — have done a lot to hurt themselves. But as the most committed parents leave, the schools may falter more, giving the larger community yet another reason to fret over their condition. "A third of our support for schools comes from property taxes," says Ray Simon, director of the Arkansas department of education. "If a large number of a community's parents do not fully believe in the school system, it gets more difficult to pass those property taxes. And that directly impacts the schools' ability to operate." Says Kellar Noggle, executive director of the Arkansas Association of Educational Administrators: "We still have 440,000 kids in public schools, and some 12,000 [in home schooling] is a small number. But those 12,000 have parents and grandparents. Sure, it erodes public support."

The thus far steep growth of home schooling does have limits, as it takes a galactic commitment of time and money and patience for a parent to spend all day, every day, relearning algebra (or getting it for the first time) and then teaching it. It's fair to assume that a majority of parents won't want to give up those delightfully quiet hours when the kids are at school. The softening economy may also begin to thin the ranks of home schoolers, many of whom are middle-class families that can't afford private schools; if stay-at-home teaching parents have to take a job, free public school will start to look very inviting.

But for now, home schooling is still growing at about 11% a year, and it's no longer confined to a conservative fringe that never believed in the idea of public education anyway. "Very different people are entering home schooling than did 20 years back," says Mitchell Stevens, author of Kingdom of Children, a history of home schooling to be published next month by Princeton University Press. According to the Federal Government, up to three-quarters of the families that home school today say they do so primarily because, like so many of us, they are worried about the quality of their children's education. A recent report by the state of Florida found that just a quarter of families in that state practice home schooling for religious reasons. The new home schoolers haven't completely given up on public education, at least not the idea of it. "The problem is that schools have abandoned their mission," says Luigi Manca, a communications professor at Benedictine University in Lisle, Ill., who home schools his daughter Nora, 17. "They've forgotten about educating."

William Bennett used to be the U.S. Secretary of Education, but today he travels the nation to preach the home-school gospel. "I'm here to talk about the revolution of common sense," he told a Denver home-schooling conference in June. Working himself up to promote K12, his slick, new, for-profit online school for home schoolers, Bennett even suggested that "maybe we should subcontract all of public education to home schoolers." It was strange to watch a man once responsible for federal aid to public schools urge people to desert them. Imagine if Colin Powell gave a speech saying we should disband the U.S. Army and assemble local militias.

But many are following. They are folks like Tim and Lisa Dean of Columbia, Md., working parents (he manages technical support for the U.S. Senate; she's a part-time attorney) who home school Bitsy, 5, and Teddy, 4. Contrary to the old picture of home schoolers, Tim doesn't leave all the teaching to his wife, and they helped start a home-school support group two years ago that includes parents who are gay and straight; black, white, Asian American and biracial; Democrat and Republican.

The conservative Christians who worked so hard in the 1980s to make home schooling legal in every state are as committed as ever, but more politically moderate Christians have also joined the movement. Susie Capraro, who home schools her son and daughter, used to be part of the Broward County Parent Support Group, the largest home-schooling network in Florida and one founded on Judeo-Christian principles. Although she considers herself a Fundamentalist Christian, Capraro didn't like group rules that keep non-Christians from leadership roles — or other exclusionary gestures, like the ice skating event that featured only Christian music. "We wanted a place where people could get the support they needed without the religion," says Capraro, who along with 10 families co-founded Home Educators Lending Parents Support. "[Religion is] not the purpose of our group, but rather to get together for the best education." Today the three-year-old organization