Teachers in Denver overwhelmingly approved an experiment linking the pay of some teachers to the academic performance of their students. Yesterday's vote marked a significant departure from the traditional opposition by teachers unions to merit pay plans.

Denver's "pay for performance" plan, as it is being called, would go a step beyond previous merit plans and, for the first time, would tie a teacher's salary directly to how well students perform in the classroom. Under past merit plans, including one in effect in Fairfax County between 1986 and 1991, salary bonuses were typically based on classroom evaluations of teacher performance--a standard that unions denounced as unscientific and subject to abuse by principals.

The two-year performance pay experiment that emerged from contract negotiations in Denver sidestepped those classic objections by making participation voluntary, limiting it to about 15 percent of the city's teachers and giving teachers a role in devising the academic standards by which their work will be judged.

After two years, teachers will have an equal say with administrators in evaluating the pilot project, and the union will have a chance to take another vote on whether to accept performance standards as the permanent basis for pay raises for the district's 4,300 teachers.

The experimental, cooperative approach has won endorsements from both national teachers unions.

"To me, it's a good example of the school district and the teachers union working together to see if they can find ways of improving student achievement," said Robert F. Chase, president of the National Education Association, the nation's larger teachers union. The Denver Classroom Teachers Association is an affiliate.

Initially, the Denver school district proposed a radical, across-the-board plan to have performance pay replace the traditional system of annual raises based on seniority. When union negotiators balked, the district revised its proposal to a one-year test before the two sides agreed on a two-year experiment.

"Up to this point, no teachers union has even been willing to experiment with this, so I say more power to them," said Laura Lefkowits, the school board member who led the push for performance pay as a way to satisfy public demands for school accountability.

Cary Baird, spokeswoman for the Denver teachers union, suggested that the nation's "entire educational system will gain from what we learn from this."

Teachers at as many as 12 elementary schools and three middle schools have a month to vote by an 85 percent majority whether to participate. Each of the approximately 450 teachers involved will immediately receive a $500 stipend and later up to $1,000 if their students meet achievement goals. In the second year, another 200 teachers at two high schools will be able to join, and teachers at all participating schools would receive as much as $1,500 for meeting their goals.

The schools will use one of three different sets of student achievement goals: scores on the standardized Iowa Test of Basic Skills, scores on skills tests created by teachers or other specially designed measures of higher achievement resulting from additional training that teachers have undergone.