The Income-Achievement Gap and Adult Outcome Inequality

This paper discusses various methods for assessing group differences in academic achievement using only the ordinal content of achievement test scores. Researchers and policymakers frequently draw conclusions about achievement differences between various populations using methods that rely on the cardinal comparability of test scores. This paper shows that such methods can lead to erroneous conclusions in an important application: measuring changes over time in the achievement gap between youth from high- and low-income households. Commonly-employed, cardinal methods suggest that this "income-achievement gap" did not change between the National Longitudinal Surveys of Youth (NLSY) 1979 and 1997 surveys. In contrast, ordinal methods show that this gap narrowed substantially for reading achievement and may have narrowed for math achievement as well. In fact, any weighting scheme that places more value on higher test scores must conclude that the reading income-achievement gap decreased between these two surveys. The situation for math achievement is more complex, but low-income students in the middle and high deciles of the low-income math achievement distribution unambiguously gained relative to their high-income peers. Furthermore, an anchoring exercise suggests that the narrowing of the income-achievement gap corresponds to an economically significant convergence in lifetime labor wealth and school completion rates for youth from high- and low-income backgrounds.