The private school sample (the "delta sample") was designed to produce a nationally representative sample among the students in private schools in the United States. Fourth- and eighth-grade students were assessed in mathematics, reading, and a pilot test. Eighth- and twelfth-grade students were assessed in writing.
The target sample sizes for each grade and subject are shown in the table below. Target sample sizes were adjusted for expected school and student response and eligibility.
|† Not applicable.
SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2007.
Samples were based on a two-stage design that involved selection of schools within strata and selection of students within schools. The first-stage samples of schools were selected with probability proportional to a measure of size based on the estimated grade-specific enrollment in the schools.