PORTLAND, Maine — High school graduation rates in greater Portland and midcoast Maine are higher than the rest of state, which overall ranked 10th in the nation, according to the first comparison data released by the U.S. Department of Education that includes a standard formula for most states.

Maine is within 4 percentage points of Iowa, which had the highest graduation rate at 88 percent. The District of Columbia had the lowest rate with just 59 percent of high school students graduating.

The data creates a standard that all but three states have accepted, allowing for more direct comparisons, Maine Department of Education spokesman David Connerty-Marin said.

Previously, states used different measurements, including factoring in GED certificates and students who took five or more years to graduate, for their total graduation numbers.

The formula also breaks down the statistics into subgroups of race, ethnicity, limited English proficiency, children with disabilities and economically disadvantaged students.

Connerty-Marin said the new formulation doesn’t affect Maine’s measurements, but now allows the state to compare itself more accurately to others and, hopefully, will help the state improve.

“It gives us the opportunity to look apples to apples how Maine is doing,” he said. “The value is not to see how we rank, but rather to see how all the states are doing, see who’s progressing and quickly assess what we can do to improve things in Maine.”

The 13 public high schools in The Forecaster’s coverage area, ranging from Scarborough to Bath, have a 2 percent lead on the state: an average 86 percent graduation rate.

Two of the highest graduation rates in the state were in Cape Elizabeth and Yarmouth, which had rates of 97 percent and 96 percent, respectively. Both schools have historically had high graduation rates and are usually within a percentage point or two of each other every year; Yarmouth held the top spot in 2010 and 2009.

School principals say graduation rates depend on several factors, but one of the most obvious correlations is between graduation and wealth.

In Cape Elizabeth and Yarmouth, the median annual family household income is about $87,000 and $65,000, respectively, according to the latest U.S. Census data. Both towns are more than $20,000 higher than the state median.

In contrast, Wiscasset, where the graduation rates are the lowest of any mainstream high school in the state, at 62 percent, 55 percent of families earn less than $50,000 a year.

Still, wealth doesn’t paint the whole picture, said Deborah Taylor, principal at Wiscasset High School, part of Regional School Unit 12.

In RSU 12, students have free school choice because of the large geographic area the district encompasses, Taylor said. The result is that a “significant” number of students end up transferring to Wiscasset High School, she said, making it more difficult to catch students before they begin to fall too far behind.

“Often things that contribute to mobility are things that coincidentally impede education: homelessness, poverty, searching for jobs, lack of security,” she said. “If a student starts somewhere else and is not successful, later in their high school career they join us and it becomes that much harder to address the situation.”

Taylor noted Wiscasset has a much higher graduation rate among students who spend all four years at the school. The area also has two alternative schools, which cater to students who have not had success in mainstream high schools, and often have lower graduation rates, she said.

Ted Hall, principal at Yarmouth High School, said socioeconomics plays a role.

“We have parents and community members that are invested and have made a commitment to education,” he said. “Partly as a result is that we set high aspirations and there’s an expectation that you’re going to graduate.”

Hall said having the ability to stay connected with students is also crucial for graduation.

“If you look at the literature on dropouts in general, often they’ll report that no one knew them, so it was relatively easy for them to drop out,” he said. “As a school we have to make sure we are connected and paying attention to them as individuals.”

One of the factors that Hall attributes to some of Maine’s success with higher graduation rates is small enrollments, which makes staying connected to students easier and the experience more personal.

At Wiscasset, Taylor said they have made efforts to boost their graduation rates by connecting to students through dropout committees, talking to younger students early and examining closely who the students are that drop out.

The district is also looking at adopting proficiency-based credit system, a shift from traditional “time-in-seat” credits, she said. This type of education allows students who have been out of school and get behind in classroom time to prove their ability in an accelerated manner.

But Cape Elizabeth High School Principal Jeffrey Shedd said graduating is not the only important factor for determining success.

“We want our kids to graduate, but more importantly we want to have our kids graduate prepared,” Shedd said, noting that 90-95 percent of students who graduate from the school go on to college. “A more important measurement is how the kids do after they leave. And that becomes a real challenge to track.”