Gill-breathing freshwater snails (Family "Pleuroceridae") are ecologically important, abundant in many streams in the United States, and easy to collect and maintain under classroom conditions. These snails can be used in classroom tests to demonstrate effects of pollutants on aquatic organisms. In more advanced classes, students can cage the snails or use tag-release-recapture methods to conduct in-stream studies on water quality. In this article, the authors describe techniques for conducting classroom and field tests with two snail genera ("Elimia" and "Pleurocera"), focusing on examples of methods that are appropriate for high school and college students interested in aquatic ecology or water-quality testing. (Contains 4 figures.)