NASHVILLE (AP) — An Associated Press analysis of student testing data shows Tennessee school systems without teachers' collective bargaining rights performed slightly better than those with negotiated contracts, but posted weaker gains.

Thirty-eight of the state's 135 local school districts did not engage in collective bargaining with their teachers before a new law eliminated those rights this year, according to the Tennessee Education Association.

Those districts averaged a higher percentage of students earning proficient or advanced scores in the four categories tested. The largest difference was in math, where non-bargaining districts averaged 3.5 percentage points higher than the rest of the districts, while social science scores were just a half percentage point apart.

But the districts that allowed collective bargaining — which included the state's four largest cities — averaged larger gains in all four categories compared with last year's scores.

The mostly Republican supporters of a new law that replaced collective bargaining rights with a concept called "collaborative conferencing" argued that the move put a priority on teacher performance over workplace issues.

But Democrats and the state's largest teachers' union characterized the legislation as a politically motivated attack.

"The data clearly shows that those legislators who said the repeal of collective bargaining would improve student achievement were either misinformed or trying to disguise their real motives," said Tennessee Education Association lobbyist Jerry Winters.

"There is little doubt that repealing the collective bargaining law had very little if anything to do with education reform but a lot to do with politics."

Sen. Jack Johnson, R-Franklin and the main sponsor of the collective bargaining repeal, said test scores alone were not the reason he sought to make the change. He said the main goal was to reduce the "hostility between the school boards and the teachers that are union members."

"Removing the exclusivity of the unions to have negotiating rights on the part of teachers means you can have more effective and more productive communication between teachers and school boards," he said. "And you're going to get a better outcome."

Republicans criticized the TEA for overwhelmingly supporting Democratic candidates but have denied that the new law was retribution for the fundraising snub.

Senate Minority Leader Jim Kyle of Memphis said the best teachers are motivated ones, and that Republican legislative efforts have served to demoralize educators.

"We have damaged education and we have damaged the morale of teachers," Kyle said. "That's what we're hearing from the people going back to work."

Republican Gov. Bill Haslam sought to remain neutral on the collective bargaining measure during the session while focusing on his own education initiatives, such as lifting a cap on charter schools and making teacher tenure more difficult to obtain. He ultimately signed the collaborative conferencing measure into law.

Haslam was asked by reporters last month whether the overall improvement in student test scores called into question the need for the slew of education initiatives passed this year. The governor said he was pleased with the better scores but stressed that the state needs to do much better.

"Obviously, I think the key things that were passed in the Legislature ... are important for keeping us on a trajectory," he said. "What the discussion should always be about is what's the best thing for the child.

"We should realize that we are making progress, but we're not where we need to be."