In the small Monona Grove School District in Wisconsin, three teachers had planned to retire this year. But then, says history teacher Thomas Howe, the "political dust-up" happened – the controversy over a law, eventually pushed through by Gov. Scott Walker (R) and supporters, that restricts public employees' collective-bargaining power.

In the midst of the battle last spring, 17 teachers, including Mr. Howe, retired from that school district. "Many of us felt very bittersweet about it," he says.

Across Wisconsin this year, teachers have opted to retire at higher rates than usual, partly in response to the new law. Under the law, teachers have to contribute a considerable chunk of their salaries to health and retirement plans, and districts can decide to lengthen the school day or year without increasing salaries.

For supporters of the legislation, it grants more flexibility to districts to prevent costs from careening out of control. Some districts have already started saving money, according to Governor Walker's office.

Moreover, the instruction at some schools may benefit from a changing of the guard, education experts say.

"To the degree this is a shift in the composition of who's in the system ... it is going to align the system more with the direction of current education reform, which I would say is good," says Allan Odden, a professor of educational leadership and policy analysis at the University of Wisconsin-Madison.

But for opponents of the law, it unfairly cuts take-home pay, batters morale, and deprives schools of droves of veteran teachers who are retiring early. "The loss of experience and the loss of qualified mentors [for new teachers] outweighs any financial gain to the districts," says Betsy Kippers, a teacher in Racine and vice president of the Wisconsin Education Association Council, a 98,000-member union.

Many states – not just Wisconsin – have been struggling to rein in the benefit costs of public employees. Indiana and Ohio both passed laws this year restricting collective bargaining for teachers and other public workers – though voters may repeal Ohio's in November.

In Tacoma, Wash., the school district's proposal to trim teacher pay, increase class sizes, and reassign teachers based on evaluations rather than strictly on seniority prompted a strike that's now in its fourth day, despite a judge's temporary order on Wednesday that the nearly 1,900 teachers return to work.

But the fiercest statewide battle has been waged in Wisconsin, where 5,000 school employees – about twice as many as in each of the past two years – are retiring this year, according to The Associated Press.

The Beloit district lost 10 percent of its teachers, filling only 40 out of 60 vacancies. And by January, Green Bay expects more than 10 percent of its teachers to have retired, the AP reports.

At the high school where Howe worked, eight teachers retired who had taught there for more than 160 years combined. "You can't replace that," he says.

If Howe had continued teaching, the law would require him to pay 5.8 percent of his salary into his retirement plan, plus a substantial amount toward health insurance, in effect reducing his take-home pay by 10 percent, he says. And class sizes are going up by 10 percent or more.

Madison schools experienced a higher-than-usual number of retirements this year – 134 teachers. Many of them said it was because of the law, but that wasn't a record high, says district employment manager June Glennon.

The retirements in many districts can also be attributed, in part, to dem-ographic shifts. This may be a peak year for teachers reaching retirement age nationwide, research has shown.

Still another factor in Wisconsin is an $800 million cut in state aid to education.

Overall, it's not clear how many retiring teachers are being replaced. But in Madison, the district has hired 260 people this year – some of them with master's degrees and years of experience, some of them new.

"What most principals say to me is that ... a lot of times, new, fresh, young ideas are great to blend with the seasoned staff," Ms. Glennon says.

Younger teachers are more apt to support new evaluation systems for faculty, pay that's tied to performance, and various accountability measures, says Professor Odden of the University of Wisconsin–Madison.

Also, school districts aren't necessarily losing the ability to teach well if more people retire, since some research shows that teachers with three to five years of experience can be as effective as longtime veterans, says Frederick Hess, director of education policy studies at the American Enterprise Institute in Washington.

The new law has already produced some cost savings, the governor's office has said. The Appleton Area School District, for instance, expects to save $3.1 million in health-insurance costs, partly because providers now have to compete.

The potential for savings in Milwaukee should be good, according to estimates by Robert Costrell, a professor of education reform and economics at the University of Arkansas in Fayetteville. He analyzed the district's health and retirement benefits earlier this year and found they cost the public an additional 74 percent of teachers' salaries, compared with a typical rate of about 24 percent in the private sector.

But as districts start to exercise their new authority under the law, there may be more fallout. While officials in Eau Claire and Oshkosh have said they'll continue to collaborate with teachers on policies, some districts have handed down "onerous, almost punitive" mandates, says Ms. Kippers, the union rep.

The New Berlin school board, for example, recently approved an employee handbook that hundreds of teachers opposed. It reduces the number of sick days, increases work hours without increasing pay, cuts back on collaboration and prep time for classes, and implements a dress code.

Despite such tensions, Wisconsin educators and politicians of all stripes are sitting down together to work on a number of education initiatives, such as improving reading and teacher evaluations. Those efforts "are focused on how to make the school system better," Odden says, "and that's more important than lingering hostility over the budget."