NASHVILLE (AP) — About two-thirds of Tennessee teachers should be allowed to opt for a smaller portion of their evaluations to be based on student testing data, according to a study released Monday.

The report by the State Collaborative on Reforming Education, or SCORE, was commissioned by Gov. Bill Haslam to review the state's new teacher evaluation system. The Republican governor asked lawmakers not to enact any changes to the system while the study was being conducted.

Fifty percent of teachers' evaluations are based on student testing data, but only about one-third teach subjects where value-added testing data is collected. The SCORE report recommends that teachers in subjects or grades without specific testing data be allowed to reduce that component to 25 percent of their evaluation.

The recommendation seeks to address concerns raised repeatedly by teachers since the evaluation measure was first enacted as part of Tennessee's federal Race to the Top grant application in 2010. Tennessee was one of the first two states selected for the grants.

Education Commissioner Kevin Huffman in a statement thanked SCORE for conducting the study, and said the department plans to submit its own recommendations to lawmakers by July 15.

"We are confident this work will improve the state's evaluation system," he said.

Democratic lawmakers unsuccessfully tried first to suspend the evaluations in their first full year.

Jerry Winters, a lobbyist for the Tennessee Education Association, said the state's largest teachers' union welcomes changes to the evaluation standards.

"The state knew all along that the lack of test data for the majority of teachers in the state was a huge weakness in the system, but they stubbornly moved forward with the evaluations this past year anyway," TEA lobbyist Jerry Winters said in an email.

"The use of school-wide test data — evaluating teachers using the data of students they may not even teach — is a blatant mistake which raises major credibility issues," he said.

SCORE was launched by former U.S. Senate Majority Leader Bill Frist, R-Tenn., and is now led by Sen. Jamie Woodson, a former Republican state senator from Knoxville. The report was based on feedback from nine roundtables and more than 16,000 teachers and administrators who participated in a statewide questionnaire.

Other recommendations include improving training for evaluators; linking evaluation results with training opportunities for teachers; accelerating a system for evaluating principals; redoubling efforts in districts where teacher evaluation systems have faltered in the first year; and integrating the evaluation system with the new common core state standards.

"The new evaluation system is nuanced and complex," the report concludes, "because the art of teaching is nuanced and complex.

"Continued improvement, over time, is critical."

Haslam said in a statement that he will consider the SCORE recommendations along with the findings of the state Education Department.

"If we want to improve education in Tennessee, that starts with an effective teacher leading each Tennessee classroom," Haslam said.