The NAEP 2006 sample design yielded a nationally representative sample of private school students in each of grades 4, 8, and 12 through the use of a three-stage approach: selection of primary sampling units (PSUs), selection of schools within strata, and selection of students within schools. The sample of schools was selected with probability proportional to a measure of size based on the estimated grade-specific enrollment in the schools.
The general targets for the private school samples were as follows:
These students were allocated among four different tests at grades 4 and 12, and five different tests at grade 8. The operational tests were in civics, economics (grade 12 only), and U.S. history. The precalibration tests were in mathematics and reading, both at grades 4 and 8 only. A pilot test in writing was conducted at grades 8 and
12 only. Target sample sizes were adjusted for expected school and student response and eligibility.
From the stratified frame of private schools for each grade, a systematic random sample of grade-eligible schools was drawn with probability proportional to a measure of size based on the estimated grade-specific enrollment of the school.
Each selected school in the private school sample provided a list of eligible enrolled students from which a systematic, equal probability sample of students was drawn.