Researchers, grant-makers and policymakers have long relied on enrollment numbers for the federally subsidized Free and Reduced-Price Lunch program. They use those numbers as a handy proxy for measuring how many students are struggling economically. The paperwork that families submit to show their income becomes the basis of billions in federal funds.

To be eligible for these programs, a family must earn no more than 85 percent above the poverty line. Just over half of public school students fit that description.

At least, that's today's figure. As Jill Barshay reports for the Hechinger Report, things are about to get more vague.

That's because of a new federal program called "community eligibility." Under that provision, a school or even an entire district can provide free lunch to all its students, as long as at least 40 percent of them qualify for a means-tested program.

That means a school could, in theory, go from 40 percent to 100 percent "free lunch" overnight.

There are solid reasons behind this initiative. If everyone partakes, it removes the stigma of free lunch. Immigrant families with issues documenting their income can still take advantage of the program.

But the potential issue is that school districts will handle their reporting differently, leaving the nation without a single, reliable measure of student poverty. About 13 percent of schoolchildren are currently receiving free lunches under the new community eligibility program, but we don't know how many of them are actually facing economic hardship.

As our colleagues at WNYC reported, Detroit is still having students fill out the old paperwork, but it's not required. Chicago, Barshay reports, has created a new form to cover eligibility like field trips and school uniforms. And Cleveland is simply reporting that everyone gets free and reduced lunch.

Earlier in the year, we explored the history of the free and reduced-price lunch program:

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