The 2001 No Child Left Behind Act (NCLB) increased accountability pressure in U.S. public schools by threatening to impose sanctions on Title‐1 schools that failed to make adequate yearly progress (AYP) in consecutive years. Difference‐in‐difference estimates of the effect of failing AYP in the first year of NCLB on teacher effort in the subsequent year suggest that on average, teacher absences in North Carolina fell by about 10 percent. The probability of being frequently absent similarly decreased. These reductions in teacher absences were driven by within‐teacher increases in effort and by teachers in the bottom half of the effectiveness distribution. On average, only a modest amount of the achievement gains attributable to the increased accountability pressure are explained by the corresponding decline in teacher absences.