The schools and students participating in NAEP assessments are selected to be representative of all schools nationally and of public schools at the state level. Samples of schools and students are drawn from participating states and from the District of Columbia and Department of Defense schools. While results for students assessed in Alaska, the District of Columbia, Kansas, Nebraska, and Vermont contributed to the results for the nation at grades 4 and 8, sample sizes were not large enough to report results for these states/jurisdictions separately. The results from the assessed students are combined to provide accurate estimates of the overall performance of students in the nation and in individual states and other jurisdictions. Results are not collected at the state level for grade 12. Because each school that participated in the assessment, and each student assessed, represents a portion of the population of interest, the results are weighted to account for the disproportionate representation of the selected sample. Read more technical information about weighting adjustments made at the school and student level.
To ensure unbiased samples, NAEP requires that participation rates for original school samples be 70 percent or higher to report national results separately for public and private schools. In instances where participation rates meet the 70 percent criteria but fall below 85 percent, a nonresponse bias analysis is conducted to determine if the responding school sample is not representative of the population, thereby introducing the potential for nonresponse bias.
Before substituting new schools for originally sampled schools that declined to participate, the weighted national school participation rates for the 2009 science assessment were 97 percent for fourth grade (100 percent for public schools, 73 percent for private schools), 97 percent for eighth grade (100 percent for public schools and 72 percent for private schools), and 83 percent for twelfth grade (86 percent for public schools and 52 percent for private schools). Weighted student participation rates were 95 percent at fourth grade, 93 percent at eighth grade, and 80 percent at twelfth grade. The nonresponse bias analysis for private schools at grades 4 and 8 showed that, while the original responding school sample may not have been fully representative, the potential bias was reduced by including substitute schools and by adjusting the sampling weights to account for school nonresponse.
State and district participation
Standards established by the National Assessment Governing Board require that school participation rates for the original state samples need to be at least 85 percent for results to be reported. In 2009, there were 47 states and jurisdictions, along with 17 districts, participating in the science assessment at grades 4 and 8 that met this participation rate requirement.
The tables below provide participation rates before substitution.
Learn more about the sampling design.