She added, “I feel like: ‘Hey, we were paying taxes all these years. This is what they were for.’ ”

Although the troubled economy is the main factor in the increases, experts said, some growth at the margins has resulted from a new way of qualifying students for the subsidized meals, known as direct certification. In 2004, Congress required the nation’s 17,000 school districts to match student enrollment lists against records of local food-stamp agencies, directly enrolling those who receive food stamps for the meals program. The number of districts doing so has been rising — as have the number of school-age children in families eligible for food stamps, to 14 million in 2010-11 from 12 million in 2009-10.

“The concern of those of us involved in the direct certification effort is how to help all these districts deal with the exploding caseload of kids eligible for the meals,” said Kevin Conway, a project director at Mathematica Policy Research, a co-author of an October report to Congress on direct certification.

Congress passed the National School Lunch Act in 1946 to support commodity prices after World War II by reducing farm surpluses while providing food to schoolchildren. By 1970, the program was providing 22 million lunches on an average day, about a fifth of them subsidized. Since then, the subsidized portion has grown while paid lunches have declined, but not since 1972 have so many additional children become eligible for free lunches as in fiscal year 2010, 1.3 million. Today it is a $10.8 billion program providing 32 million lunches, 21 million of which are free or at reduced price.

All 50 states have shown increases, according to Agriculture Department data. In Florida, which has 2.6 million public school students, an additional 265,000 students have become eligible for subsidies since 2007, with increases in virtually every district.

“Growth has been across the board,” said Mark Eggers, the Florida Department of Education official who oversees the lunch program.

In Tennessee, the number of students receiving subsidized meals has grown 37 percent since 2007.

“When a factory closes, our school districts see a big increase,” said Sarah White, the state director of school nutrition.

In Las Vegas, with 13.6 percent unemployment, the enrollment of thousands of new students in the subsidized lunch program forced the Clark County district to add an extra shift at the football field-size central kitchen, said Virginia Beck, an assistant director at the school food service.