New Jersey towns have figured out a way to tame the highest property taxes in the United States.

Keep kids out.

Educating one child in New Jersey costs an average of $12,567 a year, the most in the nation. The result: more than double the property tax parents typically pay.

So some local governments in the state have hit upon a way to expand the tax base without the expense of higher school enrollment: age-restricted housing.

New Jersey developers have responded by building an estimated one-fifth of the country's adults-only housing, making the state the leader in a national trend fueled by baby boomers' seeking new homes after their children move out.

In New Jersey, where schools can eat two-thirds of a municipal budget, building communities that don't allow children has as much to do with reducing taxes as it does with serving older homebuyers.

"It's frustration on the part of some communities," said New Jersey Gov. Corzine in a Jan. 12 interview. "The real problem is, we have too much reliance on property taxes in how we finance public education."

Nationwide, 2.8 million households were part of age-restricted communities in 2005, up 29 percent from 2001. The number in New Jersey grew 37 percent in the same period. More than half of the housing units started in the state in the last two years have excluded children, data compiled by the New Jersey Builders Association show.

In one New Jersey town, Monroe Township in Middlesex County, population 28,000, half the housing units are limited to senior citizens.

As many as 95,000 such units will be built in the United States this year, according to an estimate from the National Association of Home Builders. New Jersey developers will build about 20,000 of them, the state builders group said.

About 8 percent of homes sold by Toll Bros. Inc., the Horsham firm that is the biggest luxury home builder in the nation, now are in age-restricted communities, said Frederick Cooper, senior vice president for finance and investor relations. That's double the share from five years ago.

"We see it as a growing part of our business, especially in cold-weather markets in the Northeast that you wouldn't necessarily see as traditional places for people to retire," Cooper said.

For Pulte Homes Inc., the largest U.S. homebuilder by market value, 39 percent of its homes sold in 2005 had age restrictions, up from 33 percent in 2004, said company spokeswoman Caryn Klebba.

"Age-restricted housing is growing more than the general housing market," said Ara Hovnanian, chief executive of Hovnanian Enterprises Inc. of Red Bank, N.J., the state's largest home builder.

Age-restricted housing does help reduce property taxes, according to the New Jersey Department of Community Affairs.

In Monroe Township, which has 8,878 age-restricted units, the most in the state, the property tax averaged $4,327 in 2004, the latest year statistics were available. That was 16 percent lower than the rest of Middlesex County and 22 percent less than the state average.

By comparison, South Brunswick, Monroe Township's neighbor, has just 731 units of age-restricted housing and an average property tax of $5,782.

Exclusionary zoning is legal in the United States. A 1998 exemption to the federal Fair Housing Act allows age restrictions if homes in a development are intended solely for residents age 62 and older, or if 80 percent of the units are occupied by one person who is at least 55.

"Exclusionary zoning is most prevalent in New Jersey, but it's pervasive in a lot of parts of the country, especially in the Northeast, where there isn't a lot of land to build on," said Robert Puentes, a fellow with the Brookings Institution's Metropolitan Policy Program. "With property tax being such a big issue now, it's much more front-and-center."

There are detractors, though. For one thing, age-restricted housing can swing the balance in a community toward a population of senior citizens who need health-care services.

"The imbalance that age-restricted housing brings is going to be a disaster for the state in the long run," said Mayor Ray Coles of Lakewood Township, which has New Jersey's third-highest number of such units.

"New Jersey seems to be looking for ways to turn families away," he said. "Someday, my own kids, who are teenagers now, might have to move out of state to raise their families. I don't want to have to hop on a plane to visit my grandkids."