Preliminary results are in, and they suggest it has helped with math skills but not with reading achievement, as measured in the 4th and 8th grades. Via Thomas Dee and Brian Jacob:
The No Child Left Behind (NCLB) Act compelled states to design
school-accountability systems based on annual student assessments. The
effect of this Federal legislation on the distribution of student
achievement is a highly controversial but centrally important question.
This study presents evidence on whether NCLB has influenced student
achievement based on an analysis of state-level panel data on student
test scores from the National Assessment of Educational Progress
(NAEP). The impact of NCLB is identified using a comparative
interrupted time series analysis that relies on comparisons of the
test-score changes across states that already had school-accountability
policies in place prior to NCLB and those that did not. Our results
indicate that NCLB generated statistically significant increases in the
average math performance of 4th graders (effect size = 0.22 by 2007) as
well as improvements at the lower and top percentiles. There is also
evidence of improvements in 8th grade math achievement, particularly
among traditionally low-achieving groups and at the lower percentiles.
However, we find no evidence that NCLB increased reading achievement in
either 4th or 8th grade.
That is from an NBER paper, I do not yet see an ungated copy on-line. To my skewed perspective, this is an intuitive result. Math skills are more the result of drill, whereas you have to learn how to love to read and much of that happens within the family, not at school. Math is therefore easier to "teach by central planning," so to speak.