What is the difference between state NAEP and national NAEP?

The NAEP sample in each state is designed to be representative of the students in that state. At the state level, results are currently reported for public school students only and are broken down by several demographic groupings of students. When NAEP is conducted at the state level (i.e., in mathematics, reading, science, and writing), results are also reported for the nation. The national NAEP sample is then composed of all the state samples of public school students, as well as a national sample of nonpublic school students. In non-participating states, a certain number of schools and students are selected to complete the national-level sample.

For assessments conducted at the national level only, samples are designed to be representative of the nation as a whole. Data are reported for public and nonpublic school students as well as for several major demographic groups of students.