Gov. Phil Murphy has had a friend in the state's largest teachers union since his days on the campaign trail.

Now, top lawmakers in his own party are accusing him repaying the union with a wet kiss of a political favor.

The state Department of Education on Friday announced it's slashing the weight of standardized test results in teacher evaluations from 30 percent to 5 percent. The move was celebrated as "a big win" by the New Jersey Education Association, the union that backed Murphy and lobbied for softening the impact of standardized test results on teachers.

At the same time, Murphy's maneuver was panned by top Democratic lawmakers who had pushed for using student performance on standardized tests as a factor in evaluating teachers.

"These tests are about education, not politics," Senate President Stephen Sweeney, D-Gloucester, and Sen. Teresa Ruiz, D-Essex, said in a statement. "This is a victory for special interests and a huge step backward towards a better public education in New Jersey."

In the classroom, the decision affects about 20 percent of the state's teachers. Standardized test results are used only in the evaluations of those who prepare students for the state math and English exams. Teachers of different grades or subjects are not affected. Those teachers, who work in elementary and middle schools, will now have their evaluations based more heavily on administrators' observations and other goals established by their principals.

In the Statehouse, Murphy's move added to existing criticism that his education policy is being dictated by the NJEA. It also generated another dispute with Sweeney, who has clashed with the governor and feuded with the powerful union.

Realistically, the change might have little effect on teachers' overall ratings. Almost all teachers received positive reviews both before and after the state began considering test results as a determining factor.

Grading teachers

Instead of simply using students' overall test scores, the state measures how much students are improving from year to year when compared to other students across the state with similar academic backgrounds.

So, a teacher with students who score highly overall could be hurt if the students don't improve enough, and a teacher whose students perform poorly could be helped if they make notable gains despite their low scores.

The state started using student performance on standardized tests as a weight in some teachers' evaluations beginning in the 2013-14 school year, part of New Jersey's landmark tenure reform law. It initially counted for 30 percent of teachers' evaluations, but Gov. Chris Christie cut it to 10 percent during the first year of PARCC exams in 2014-2015.

Christie later raised the weight back to 30 percent prior to the 2016-17 school year.

The NJEA has argued that the state exams are flawed tests that students don't take seriously and should not be used to evaluate teachers.

"By dramatically lowering the stakes for the test, Murphy is making it possible for educators and students alike to focus more time and attention on real teaching and learning," NJEA President Marie Blistan said.

Democrats disagree

Murphy, a Democrat himself, was able to make the move without legislative approval because the weight of test results in teacher evaluations is up to the state education commissioner.

The new governor previously announced plans to reduce the weight of test results in teacher evaluations but did not say how low he would go. The administration officially made the changes in a memo sent to districts Friday.

Sweeney and Ruiz, chair of the Senate Education Committee, said they want answers for why Murphy is seemingly lowering standards.

"We look forward to the department providing data as to why these decisions are being made and how they will benefit our children," they said in a statement.

Adam Clark may be reached at adam_clark@njadvancemedia.com. Follow him on twitter at @realAdamClark. Find NJ.com on Facebook.