Cognitive and affective outcomes of a class visit to a participatory science museum were examined by comparing responses of 416 fifth and sixth graders randomly assigned to four conditions (control, exhibit only, lesson only, and exhibit followed by lesson) and two tests (verbal and visual). Students visiting a simple machines exhibit scored higher on a test of science content than the control group, but lower than the group attending a classroom lesson in the museum. The study did not demonstrate conclusively a cognitive advantage of having the exhibit experience prior to the lesson. Scores on the visual test were consistently higher than scores on the verbal test. Study findings indicate that the particular strength of the science museum exhibit lies in the affective domain. Students found the exhibit much more enjoyable, interesting, and motivational than a classroom lesson. Implications of the findings for science education are discussed.