A State Supreme Court Judge partially sided with the state teachers union today over how big of a role standardized state test scores should play for teacher evaluations.

Overturning a key state regulation that was approved by the Board of Regents in May, Judge Michael Lynch ruled that local districts could only double the weight of test scores in evaluations – from 20 percent to 40 percent – if the local union signs off on the arrangement. The judge upheld a different regulation, which will allow districts the option to increase testing emphasis, so long as it is through collective bargaining.

The New York State Education Department criticized the judge’s reversal and pledged to appeal it, further complicating the future of an evaluation system that was originally slated to take effect this year.

The decision came in response to a lawsuit filed by New York State United Teachers in June. In the suit, NYSUT lawyers argued that the Regents were circumventing a carefully negotiated state law that set the weight of test scores at 20 percent.

The law, which NYSUT backed, mandates that student growth count for 40 percent of a teacher’s rating. It set 20 percent as based on student test scores and the other 20 percent on “local assessments” chosen by districts and their unions. This spring, the Regents said districts could fill the second 20 percent in with test scores, even without union consent. NYSUT sued over that rule, and not the law itself.

Today, the judge agreed with NYSUT that state tests should not be allowed to count for the local assessment as well. In his decision, Lynch wrote that the state law clearly notes that the student growth should include “multiple measures of effectiveness.”

In an interview, NYSUT President Richart Iannuzzi called the ruling a “victory for the value of collective bargaining.”

“There’s no question that the state education department imposed regulations that the law explicitly left to local collective bargaining and the judge in no uncertain terms said they were wrong,” Iannuzzi said.

But in a press release announcing his plan to appeal the ruling State Education Commissioner John King said the ruling means that teachers whose students didn’t advance could still get positive evaluations.

“If we’re serious about supporting excellence in teaching, we can’t have an evaluation system that permits a teacher who scores a zero on student achievement to receive a positive rating,” SED Commissioner John B. King, Jr. said.

The decision could effect the partial teacher evaluation agreement reached by New York city education and union officials last month, a Department of Education spokesman said today. Most of the 33 “transformation” schools chosen to pilot new evaluation models this year are based entirely on classroom observations, but eight will evaluate teacher using test scores.