Interest in using classroom experiments to teach economics is increasing whereas empirical evidence on how experiments affect learning is limited and mixed. The author used a pretest-posttest control-group design to test whether classroom experiments and grade incentives that reward performance in experiments affect learning of introductory microeconomics. The author measured the partial effects of experiments independently of instructor quality and teaching methods using Test of Understanding in College Economics scores. Experiments without incentives are associated with higher posttest scores and greater improvement over pretest scores, but grade incentives may offset benefits of experiments. Controlling for student aptitude and other characteristics, limiting influence of potential outliers, or adjusting for potential selection bias from incomplete observation of test scores does not alter the conclusion that experiments increase learning whereas grade incentives do not. (Contains 2 figures, 4 tables and 28 notes.)