DENVER -- Denver became the largest school district in the country to switch to paying teachers based on their students' achievement as voter approved an annual $25 million tax increase to link teacher salaries to test scores and other measurements.

With 100 percent of precincts reporting, 61,724 voters, or 58 percent, voted for the Professional Compensation system measure, while 42 percent, or 44,006, voted against it.

New teachers automatically would be placed in the ProComp system. Current teachers could choose whether to participate and they will have seven years to decide. The raises would be funded with a $25 million annual tax increase which would have each household pay about $24 per year per $100,000 of the home's value, or an average of $60 in property taxes for the average homeowner.

Opponents argued the system would result in inequities because it would allow subjective decisions by administrators to justify giving -- or not giving -- a raise.

Retired state government worker Darrell Gorre, 53, said he voted for the proposal in large part because of the city's relatively high cost of living.

"We're paying someone to teach our kids a low salary and they have to live someplace that's expensive," he said. "That's no way to try to keep teachers."

Some parents had mixed feelings, but most voiced support for the idea.

"I just tried to see if that was a good thing for the teachers, if this was a good investment overall out of my pocketbook," said parent Janet Stinson.

"I think it's an extremely important issue to put more funding in areas that have been neglected in the past, and that's personally why I'm in support of it," said parent Rhiannon McGaw.

"I think that our teachers are underpaid as it is and we find money for everything else. We need to find money to get kids a good education because tomorrow it's going to be all about them," said parent Yolanda Johnson.

Education experts have said the vote was being closely watched around the nation. Unions have balked at pay-for-performance plans elsewhere, but the Professional Compensation system proposal was drawn up by the Denver Classroom Teachers Association and district administrators. Denver Mayor John Hickenlooper was a strong supporter. The teachers union and school officials also worked together on a four-year pilot program to work out some of the kinks for staff and the district's 4,000 teachers.

Under ProComp, teachers would earn a base salary of $33,301, with raises based on advances in four categories: knowledge and skills, a professional evaluation, market incentives and student growth.

Teachers could earn almost $3,000 more per year after getting a graduate degree or national license, or $1,000 more annually for working in hard-to-serve schools, where poverty is often higher and test scores often lower, or hard-to-fill positions such as math and science.

Eventually, teachers in the ProComp system could make about $33,000 more annually at the end of their careers than teachers in the current system, organizers say.