The No Child Left Behind Act (NCLB) has been criticized for encouraging schools to neglect students whose performance exceeds the proficiency threshold or lies so far below it that there is no reasonable prospect of closing the gap during the current year. We examine this hypothesis using longitudinal data from 2002–03 through 2005–06. Our identification strategy relies on the fact that as NCLB was phased in, states had some latitude in designating which grades were to count for purposes of a school making adequate yearly progress. We compare the mathematics achievement distribution in a grade before and after it became a high-stakes grade. We find in general no evidence that gains were concentrated on students near the proficiency standard at the expense of students scoring much lower, though there are inconsistent signs of a trade-off with students at the upper end of the distribution.