by Sally Holland, CNN

Washington (CNN) – The number of “dropout factory” high schools in the United States is decreasing, according to a report from the Building a Grad Nation Summit being held this week in Washington.

Between 2009 and 2010, the number of “dropout factories” – the term used in the report for those high schools that graduate 60% or less of the number of freshmen who reported for class four years earlier – dropped from 1,634 to 1,550, continuing a trend that has accelerated in recent years, the report says.

It is estimated that around one-quarter of students in the United States do not complete high school. The Grad Nation campaign has a goal of attaining a 90% graduation rate by the year 2020.

Only the state of Wisconsin currently reaches that benchmark, although Vermont is less than half a percentage point away, the report says.

“The good news is that some states have made improvements in their graduation rates, showing it can be done,” said Robert Balfanz, one of the report’s authors. “But the data also indicate that if we are to meet our national goals by 2020, we will have to accelerate our rate of progress, particularly in the states that have shown little progress.”

Over the past decade, the report says, the number of high schools considered “dropout factories” has declined by 457, with the largest decrease coming since 2008.