The Brookings Institution | April 13, 2017

Susan M. Dynarski and Katherine Michelmore

The gap within the gap

Researchers and policymakers devote considerable effort to understanding gaps in academic achievement between low-income students and their better-off classmates. And rightly so: the income-based achievement gap is a large and growing source of educational inequality in the United States. The test-score gap between high- and low-income students is 40 percent wider today than it was 25 years ago.

One widely-used marker for poverty in schools is a student’s eligibility for free or reduced-price lunch. But while nearly half of students nationwide are eligible for subsidized meals, only a quarter of US children live in poverty. These two statistics make clear that eligibility for subsidized meals is a blunt measure of economic disadvantage. This rough measure may be perfectly appropriate for determining which children should receive school lunch subsidies, but it may be less useful for other purposes, such as measuring income gaps in achievement, determining the effectiveness of educational interventions targeted to low-income families, or steering resources toward the neediest children. Yet it is, for now, the only measure available to the many researchers and practitioners who work with administrative data to evaluate the effects of educational programs, measure gaps in student achievement, and steer resources toward the neediest children.

We use administrative data from Michigan to develop a more detailed measure of economic disadvantage. Our data contain information on the entire population of students in the Michigan public schools. We leverage the longitudinal nature of these data to document systematic variation in outcomes within the population of children who are eligible for subsidized meals. We do this by counting the number of years in which a given student qualified for subsidized meals, over multiple years of school enrollment.

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