A researcher at Lumen university would like to test the impact of two teaching methods on students' achievement in an introductory statistics course. The researcher selects subjects randomly from the population of students who enrolled in the introductory statistics course and assigned them to two blocks of four such that each student has the same undergraduate class standing (freshman, sophomore, junior, and senior). Within each block, each student is randomly assigned to a different teaching method. At the end of the semester, the researcher collects the student's final grade in the introductory statistics course.

What is the blocking variable?

• Lumen university
• Lumen university students who enrolled in the introductory statistics course
• The introductory statistics course
• The teaching methods
• Student's undergraduate class standing
• Student's final grade in the introductory statistics course