For March, I’m planning a series of posts looking at NAEP by the numbers. The first two numbers are 20 and 10, as in the 20 students performing at the 10th percentile in reading and mathematics in a typical NAEP state sample. We’re all concerned that the bottom has been falling out of NAEP results, but my question is just how well we understand who those 10th percentile students are.
The 10th percentile sitting out there 1.28 sd from the mean is kind of an abstract concept, but a classroom-size sample of 20 kids is something we should be able to wrap our heads around.