The 2005 national assessment included four components:
reading and mathematics assessments of fourth- and eighth-grade students in public schools,
science and science bridge studies of fourth- and eighth-grade students in public schools,
reading, mathematics, science, and science bridge studies of twelfth-grade students in public schools, and
reading, mathematics, science, and science bridge studies of fourth-, eighth-, and twelfth-grade students in private schools.
The sample was designed to achieve a nationally representative sample of students in the defined populations who were enrolled at the time of assessment. The selected samples were based on a two-stage sample design:
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.
For the reading and mathematics assessments in fourth- and eighth-grade public schools, the samples were the state assessment samples for each jurisdiction. The science assessment for fourth- and eighth-grade public schools were also the samples from the state assessment, with a supplemental sample drawn to represent the eight jurisdictions that did not participate in the science assessment at the state level.