The NAEP national science sample is a nationally representative school and student sample for the science operational assessment. Since most jurisdictions participated in the 2005 state science operational study, the cumulated state samples provide state-level estimates and also provide an adequate nationally representative sample. A supplemental national sample was required only for the jurisdictions which chose not to participate in the state science operational study in order to represent these states in the context of a national sample. The jurisdictions which did not participate in the state science operational assessment and thus require selection of a science operational student assessment sample were
The target sample sizes for the supplemental national science operational study were 2,000 students in each grade.
An additional component of the national sample for fourth- and eighth-grade public schools in NAEP 2005 was a science assessment to provide a bridge to the 2000 NAEP science study. The target sample sizes for the science bridge study were 10,800 students in each grade. A pilot study was also conducted with target sample sizes of 4,050 for fourth grade and 4,500 for eighth grade.
The overall assessment targets for these three student samples are 16,850 for the fourth grade and 17,300 for the eighth grade. These targets were adjusted to allow for school and student attrition (nonresponse and ineligibility) based on estimates derived from the NAEP 2002 field test and equating study; the last time NAEP has carried out a special fourth- and eighth-grade national sample in addition to the NAEP state assessment. An extra factor was added to the targets to allow for some volatility in attrition.
The samples for the national science operational and the science bridge studies are commonly referred to as the "beta" samples. The beta school samples were designed to have minimum overlap with the school sample for the reading and mathematics assessments. Unlike the NAEP state assessment, school participation was voluntary.