“Clear progress is being made,” said former West Virginia governor Bob Wise, who now heads the Alliance for Excellent Education, pictured here in a file photo. (AJ Chavar)

The U.S. high school dropout rate has fallen in recent years, with the number of dropouts declining from 1 million in 2008 to about 750,000 in 2012, according to a new study to be released Tuesday.

The number of “dropout factories” — high schools in which fewer than 60 percent of freshmen graduate in four years — declined significantly during the same period, according to the study by a coalition of education groups.

“Clear progress is being made,” said Bob Wise, a former West Virginia governor who heads the Alliance for Excellent Education, one of the organizations that published the study. “It’s not a total success yet. We shouldn’t take a victory lap. But we can at least start warming up.”

The new dropout data is not surprising because the nation’s high school graduation rate has been steadily rising. Eighty-one percent of the Class of 2013 graduated on time, the highest since states began calculating graduation rates in a uniform way in 2010.

Education Secretary Arne Duncan has said the improving graduation rate serves as evidence that the nation’s public schools are making progress. But there are many reasons that graduation rates can rise, and not all of them have to do with stronger schools preparing more students for life after high school.

Alabama, for example, made outsize gains in 2014: Its graduation rate jumped more than six percentage points, the ­second-biggest increase in the nation. But the increase coincided with a policy change that took hold the same year: Alabama students no longer had to pass a high school exit exam to earn a diploma.

So what looks like a major improvement stemmed at least in part from an easing of requirements.

“There were students who had failed . . . and as a result we had some children who should have been graduating who were not graduating,” said Linda Felton-Smith of the Alabama State Department of Education.

It also is not clear how many students are graduating with the skills they need for the workplace or for college. Graduation requirements vary widely across states, and many states offer multiple levels of diplomas with different requirements.

Arizona students can earn a standard diploma that requires four courses in math, four in English and three in science, according to Achieve, a nonprofit organization that has studied graduation requirements in each state. But Arizona students also can earn a “Grand Canyon” diploma, which requires just two courses each in math, science and English — less than many colleges require for admission.

Like most states, Arizona doesn’t publicly report how many of its graduates earn each diploma type, according to Achieve. And that makes it hard to know how many students are graduating with the skills they need, said Alissa Peltzman, Achieve’s vice president for state policy.

“It’s better to have a diploma than not,” Peltzman said. “Unfortunately, far too many students graduating from high school are not ready to enter postsecondary education, the military or the workforce.”

Duncan said in an interview that the ultimate measure of success is how many students graduate from high school and don’t need to take remedial classes in college. But he said the progress that the nation is making is real, particularly regarding the decline in the number of dropout factories, which numbered just more than 1,000 in 2014, down from 2,000 a dozen years before.

“The fact that it’s been cut in half is huge,” Duncan said. “We chose to eradicate polio and did that. The goal over the next five years should be to eradicate dropout factories.”

Wise said that the graduation rate matters because students don’t have a chance if they don’t earn a high school diploma. He credited Duncan’s policies with driving improvements, and also pointed to a Bush-era 2008 regulation that required states to take action in schools where subgroups of students had chronically low graduation rates.

Wise said that federal directive spurred action, but Congress appears poised to get rid of the rule — along with many others — as it rewrites No Child Left Behind, the main federal education law.

The House and Senate have each passed their own versions of a bill that would require states to report graduation rates, but does not require the states to take action. Wise wants to see action required in schools where fewer than two-thirds of students graduate on time.

“I understand if you feel that the rest of the car is duct-taped and sputtering down the road,” Wise said of the education law. “This is actually a piece of the car that’s working well, and I don’t think you want to junk it.”

A previous version of the story implied that Education Secretary Arne Duncan was responsible for a 2008 federal regulation related to improving graduation rates. Duncan did not take office until 2009; the regulation came from the administration of President George W. Bush.