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 accellerated 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.

The Obama administration has targeted such schools with School Improvement Grants, which provide money to school districts that agree to follow certain criteria, such as closing down underperforming schools or changing a certain percentage of staff at those schools.

The grants have been criticized by those who say they don’t take into account the realities of rural school districts where it is hard to replace those staff members let go.

According to the report, the battle to meet the goal of a 90% national high school graduation rate by the year 2020 will be won or lost in 13 states that have the largest number of students to get back on track to graduate.

Those states are Arizona, Arkansas, California, Connecticut, Illinois, Indiana, Michigan, Mississippi, Nevada, New Mexico, Oklahoma, Virginia and Washington.

Tennessee and New York are the states that have shown the largest jump in graduation rates since the annual study began in 2002.

To increase high school graduation rates, the report recommends a focus on the middle schools that feed “dropout factory” high schools so that students begin their high school years with the reading skills needed to complete high school.

The Building a Grad Nation report is produced annually by Civic Enterprises, the Everyone Graduates Center at Johns Hopkins University, the America’s Promise Alliance and the Alliance for Excellent Education.