Maine has slipped six places in the latest annual ranking of the nation’s education systems.

The survey, by the publisher of Education Week magazine, cited a lack of clarity in Maine’s academic standards and few in-state examples of using students’ performance to evaluate teachers, among other factors.

While Maine’s raw score in the 2011 Quality Counts survey changed little, the state’s ranking fell to 27th in the report, which grades the 50 states and Washington, D.C., in six policy areas, including academic standards, teacher quality, school finances and overall achievement. Maine ranked 21st in 2010.

The survey could prove useful for informing policy makers, said Steve Bowen, a senior policy adviser on education issues to Gov. Paul LePage. “It’s good to get someone from outside looking over our shoulder and seeing what we’re doing.”

Maine ranked in the top tier of states on overall student achievement, 15th; school finance policies, 10th; and policies that emphasize smoother transitions to pre-kindergarten, school, the workplace and college, 11th.

But the state’s standing on policies that emphasize the quality of academic standards and teacher quality brought down its standing overall.

“The accountability is the key piece,” Bowen said. “We don’t close failing schools. We don’t fire ineffective teachers.”