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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 each state and from the District of Columbia and Department of Defense schools. 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. This includes oversampling of schools with high concentrations of students from certain racial/ethnic groups and the lower sampling rates of students who attend very small schools. Read more technical information about weighting adjustments made at the school and student level.
National participation
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. Nonresponse bias analyses were conducted for the private school samples at both grades.
The results of the nonresponse bias analyses showed that, while the original responding school samples may not have been fully representative, including substitute schools and adjusting the sampling weights to account for school nonresponse were at least partially effective in reducing the potential for nonresponse bias. However, some variables examined in the analysis still indicated potential bias after nonresponse adjustments. For instance, smaller schools were somewhat overrepresented in the final private school samples at both grades, and the responding sample of private schools at grade 8 contained a higher percentage of Black students and a lower percentage of White students than the original sample of eligible private schools.
Before substituting new schools for originally sampled schools that declined to participate, the weighted national school participation rates for the 2011 mathematics assessment were 97 percent for grade 4 (100 percent for public schools and 74 percent for private schools), and 98 percent for grade 8 (100 percent for public schools and 74 percent for private schools). Weighted student participation rates were 95 percent at grade 4 and 93 percent at grade 8.
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 2011, all 52 states and jurisdictions, along with all 21 districts participating in the Trial Urban District mathematics assessment at grades 4 and 8 met this participation rate requirement. Weighted student participation rates for TUDA ranged from 89 percent to 97 percent at grade 4 and from 84 percent to 96 percent at grade 8.
The tables below provide participation rates before substitution.
Learn more about the sampling design.
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