Income, schooling, and ability: Evidence from a new sample of identical twins

We develop a model of optimal schooling investments and estimate it using new data on approximately 700 identical twins. We estimate an average return to schooling of 9 percent for identical twins, but estimated returns appear to be slightly higher for less able individuals. Simple cross-section estimates are marginally upward biased. These empirical results imply that abler individuals attain more schooling because they face lower marginal costs of schooling, not because of higher marginal benefits.