Newly released data show that Maine’s high school graduation rate declined between the 2007-’08 and 2008-’09 school years.

But because the fall coincides with a new method of calculating the rate, it’s unclear whether fewer students are graduating.

The Maine Department of Education released statewide and school-by-school graduation rates for the 2008-’09 academic year Monday.

Some 80.4 percent of all students who began high school in the fall of 2005 had graduated four years later, the data show. That’s a drop from the 83.5 percent graduation rate the Department of Education reported for 2007-’08.

However, the 2007-’08 rate was calculated with a formula that took into account students who took more than four years to graduate but still received conventional diplomas.

The newest rate reflects only the percentage of students who graduated in four years or less, or who completed their coursework during a summer session after their fourth year.

“The value in this method is that it puts every state on the same page,” said David Connerty-Marin, a spokesman for the Department of Education. “We can compare: Who’s successful in what areas and how? What are we not doing well? And what can we do about it?”

The Education Department is shifting to a “cohort method” for calculating graduation rates, in accordance with the federal No Child Left Behind law,. The legislation requires that all states use the same method in time to report their 2009-’10 graduation rates, to make state-by-state graduation rates comparable.

For some schools, the newly calculated rate was good news.

Carrabec High School in North Anson showed a jump of more than 8 percentage points, reporting a 73.5 percent rate for the 2008-’09 year and 65.1 percent for 2007-’08.

But Kenneth Coville, the district superintendent, who was the school’s principal until last month, hesitated to draw conclusions. “It’s difficult to draw comparisons because you’re not comparing apples to apples anymore,” he said.

The new method of calculating graduation rates forces schools to report students who take unconventional paths to graduation as dropouts, he said.

The Department of Education’s position “is that students should have flexibility to graduate in less than four years or sometimes in more than four years,” he said. “But simultaneously, they use a methodology that is contradictory to that policy position.”

The revised calculation caused a significant drop in some schools’ rates. At Deer Isle-Stonington High School, for example, the graduation rate fell to 57.5 percent in 2008-’09, from 80.4 percent in 2007-’08.

While Maine reports its graduations rates to the federal government, a 26-member group is working on a separate graduation rate calculation that Maine can use to meet the objectives set out in a bill passed this year.

That law requires a 90 percent statewide graduation rate by 2016. The 26-member group will make its recommendation on calculating that rate by Nov. 1.

“I hope we come up with strong recommendations on how we incorporate these five- or six-year students who do graduate so we can accurately paint a picture of what our K-12 system is doing,” said Sen. Justin Alfond, D-Portland, the bill’s sponsor.

That picture might include counting students who earn GEDs and diplomas through adult education programs, Alfond said.