The purpose of this study was to investigate learning in a science exhibition in order to further develop the theory of science centre education as a form of informal education. In studying motivation the model of Engestr”m (1984) was used. This model separates intrinsic, instrumental and situation motivation. The subjects (N:130) of this study consisted of six comprehensive school classes of 7th graders in the greater Helsinki area. The design of the study was quasi-experimental with two different pre-treatment groups (intrinsic vs. instrumental motivation). The situation motivation group was the control group. The classes were tested by a common intrinsic/instrumental motivation test, and by a specific situation motivation test measuring the exhibition experience. The knowledge test measured the effects of a pre-lesson, the learning of isolated facts and the learning of entities. Common motivation tests were administrated three times and others twice: the pre-test three months before (T0), the post-test three days after (T1), and the delayed post-test six months after (T2) the exhibition visit. The groups were homogeneous in terms of instrinsic and instrumental motivation before the treatments. The intrinsic treatment group was the most positively motivated towards the exhibition. The difference from other groups was statistically significant (.05) and long-lasting. The results showed that the intrinsic treatment group did best in nearly all cognitive tests. In particular, the group's ability to learn entities suggests deep learning strategy. The situation motivation group performed better than expected. These results indicate that instrumental motivation does not apply to informal learning. Finally, the results confirm the theory of intrinsic, instrumental and situation motivation at least in informal education. The science centre exhibition turned out to be a motivating setting for learning. It would be instructive to apply the results to formal education.