​NAEP Technical DocumentationSchool Sample Selection for the 2019 Fourth- and Eighth-Grade Public School National Science Assessment

			Computation of Measures of Size School Sample Sizes: Frame and New School

The sampled schools for the fourth- and eighth-grade public school national assessments in science came from two frames: the primary public school sample frame constructed from the Common Core of Data (CCD) and the supplemental new-school sample frame. Schools were sampled from each school frame with probability proportional-to-size (PPS) using systematic sampling. Prior to sampling, schools in each frame were sorted by the appropriate implicit stratification variables in a serpentine order. (For details on the implicit stratification variables used for these samples see the stratification page.) A school's measure of size was a complex function of the school's estimated grade enrollment. Only one hit was allowed for each school.

Schools from the CCD-based frame were sampled at a rate that would yield a national sample of 25,200 assessed students at grade 4 and 26,100 at grade 8. Schools from the new-school frames were sampled at the same rates as those from the CCD-based frames.

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