Domain testing is a stratified sampling strategy for choosing a few test cases from the near infinity of candidate test cases. The strategy goes under several names, such as equivalence partitioning, boundary analysis, and category partitioning. This paper describes a risk-focused interpretation of domain testing and some results (experiential and experimental) of helping students learn this approach. A substantially longer version of this paper is available at www.testingeducation.org/articles/teaching_domain_testing.pdf.