The 2018 NSSME+ used a stratified, two-stage probability sample of schools and science, mathematics, and computer science teachers in grades K–12 in the United States. In the first stage, 2,000 elementary and secondary schools were selected within sampling strata with probability proportional to size. In the second stage, 10,000 science, mathematics, and computer science teachers were sampled at predetermined rates to ensure the required number of teachers for domain estimates, such as for particular regions or types of communities.
The target population for the teacher sample consisted of teachers in eligible schools who teach science and/or mathematics and/or computer science. The sampling frame for the teacher sample in each stratum (e.g., high schools) was constructed using lists of teachers and their teaching assignments. Oversampling of teachers of advanced science mathematics, and computer science was done in order to provide separate results for the various subgroups.