A statistics teacher has 4 periods of introductory statistics. She wants to get students’ opinions on a new homework policy. To get a sample, the teacher groups the students by their class performance (A students, B students, etc.). Then she randomly selects 3 students from each class performance group to survey. Which sampling method was used?

The teacher first divides students into groups based on class performance, then randomly selects students from each group. This is stratified random sampling: the performance groups are strata, and some students are sampled from every stratum. Cluster sampling would select whole groups rather than a few students from each group.

AI-written and checked against the verified answer.