High-stakes achievement testing is a centerpiece of education reform. Children from socially disadvantaged backgrounds typically perform more poorly than their more advantaged peers. The authors evaluated 91 fifth-grade children from low-income urban schools using clinical neuropsychological tests and behavioral questionnaires and obtained fourth-grade scores on state mandated standards-based testing. Goals were to determine whether executive functions are selectively diminished in children from poor urban environments and to evaluate to what extent integrity of executive functions is associated with test scores. Neuropsychological variables (particularly executive functions) accounted for 40% of the variance in English scores and 30% in mathematics. Efforts to improve children's academic achievement should consider developmental factors as well as curricular content.