The problem is most acute in Mississippi where 71 percent of students were in that category, according to the report from the Southern Education Foundation.

The group identified the share of students from low-income families by analyzing 2013 federal data on children who qualify for free or reduced lunch at school, which is offered to those from families at or below 185 percent of the federal poverty level. For a family of four, the poverty level is less than $24,000 a year and 185 percent of that figure is about $44,000.

The foundation said the share of poor students in the nation's schools has been growing for decades.

It called the fact that a majority of U.S. students are now from low-income families a "defining moment in America's public education." The group argues poor students have greater needs and should receive more support than has been offered to them.

A 2013 report from the Southern Education Foundation based on statistics from two years before found 48 percent of U.S. public school students were low-income.

In 2000, about 40 percent of the nation's public school population was low-income, according to a previous report from the organization.

The organization has for years found the greatest poverty among students in the South and the West. In California, the nation's most populous state, 55 percent of students qualified for free or reduced lunch in 2013.

By comparison, New Hampshire in the Northeast had the lowest rate at 27 percent.

(Reporting by Alex Dobuzinskis; Editing by Curtis Skinner)