The researchers suspect this trend may point to an underlying challenge for the poor: Food stamps, given out in a lump sum at the start of each month, run out for many families before they reach the end of it. Grocery stores in poor neighborhoods often report a rise in business when food stamps are electronically debited, and hospitals may see the result when they run out.

That paper, led by Hilary Seligman, is one of several relatively new studies suggesting that the level of food assistance we give families — the average family of three gets $374 a month — isn't enough for a month's worth of meals. A new report from the White House Council of Economic Advisors corralling this research shows that the short-term effects show up in some surprising ways. Amid the well-documented long-term effects of food stamps in alleviating hunger and easing poverty, week to week it looks as if the food stamp cycle may also influence hospital admissions, student test scores and even childhood behavior.

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That California study, for instance, found that the risk of hospital admission for hypoglycemia was 27 percent higher for low-income people in the last week of the month than the first week:

It's hard to test the impact of food stamp benefits — now called the Supplemental Nutrition Assistance Program — by comparing families who receive them to families who don't, since those two groups differ in a lot of other ways, too. For that reason, studies like this one are particularly useful because they track what happens to the same people over time as their benefits rise and fall.

Research also suggests that the type of food families buy doesn't change much over the course of a month. So the issue isn't simply that people splurge on high-cost items when they're flush at the start of the month, leaving them without money at the end of it. The quality of diets doesn't change, but caloric intake does: Studies have estimated that calories fall by 10-25 percent for food stamp recipients from the start to the month to the end of it.

Another new paper by Anna Gassman-Pines and Laura E. Bellows at Duke University looked at the timing of food stamp benefits and student test scores in North Carolina (North Carolina distributes benefits across the month according to Social Security number instead of on a single date). Math scores for third- through eighth-graders, they found, appear to peak around days 20-24 in the food stamp cycle, while reading scores peak from days 15-19:

Those patterns suggest that children perform best when their families receive their benefits two to three weeks before achievement tests, while they may be preparing for them.

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Another working paper, by Lisa Gennetian at the National Bureau of Economic Research and researchers at the University of Chicago, looked at disciplinary data among fifth through eighth graders in the Chicago public school district. Children from families who received food stamps had higher rates of disciplinary incidents than children from families who didn't. But the gap between the two groups widened as the end of the month approached.