WASHINGTON – U.S. public high schools have reached a milestone, an 80 percent graduation rate. Yet that still means 1 of every 5 students walks away without a diploma.

Citing the progress, researchers are projecting a 90 percent national graduation rate by 2020.

Their report, based on Education Department statistics from 2012, was to be presented ­Monday at the Building a GradNation Summit.

The growth has been spurred by such factors as a greater awareness of the dropout problem and efforts by districts, states and the federal government to include graduation rates in accountability measures. Among those efforts are closing "dropout ­factory" schools.

In addition, schools are taking aggressive action, such as hiring intervention specialists who work with students one on one, to keep teenagers in class, ­researchers said.

Growth in rates among black and Hispanic students helped fuel the gains. Most of the growth has occurred since 2006 after decades of stagnation.

"At a moment when everything seems so broken and seems so unfixable … this story tells you something completely different," said John Gomperts, president of America's Promise Alliance, which was founded by former Secretary of State Colin Powell and helped produce the report.

The rate of 80 percent is based on federal statistics primarily using a calculation by which the number of graduates in a given year is divided by the number of students who enrolled four years earlier. Adjustments are made for transfer students.

In 2008, the Bush administration ordered all states to begin using this method. States previously used a wide variety of ways to calculate high school­ ­graduation rates.

Iowa, Vermont, Wisconsin, Nebraska and Texas ranked at the top with rates at 88 percent or 89 percent. The bottom performers were Alaska, Georgia, New Mexico, Oregon and Nevada, which had rates at 70 percent or below.

Idaho, Kentucky and Oklahoma were not included because these states received federal ­permission to take longer to roll out their system.

The new calculation method allows researchers to individually follow students and chart progress based on their income level. By doing so, researchers found that some states are doing much better than others in getting low-income students — or those who receive free or reduced lunch meals — to graduation day.