According to Reinmann-Rothmeier and Mandl (2001), learning environments should provide an ideal balance between constructivist and instructive elements. Most interesting for constructivist learning processes is the combination of the cognitive and the motivational domain. In an empirical study with 207 fifth-graders of the highest stratification level, we evaluated three different approaches to the learning process based on a visit to the Natural History Museum in Berlin: the three approaches were principally characterised by closed, open and mixed tasks. One objective of our study was to assess learning achieved through the visit and the effect of different treatments. Another goal was to evaluate the motivation of the three treatment groups. We conducted a pre/post-test study with follow-up measurement. The test instruments consisted of 26 open and closed questions in the cognitive domain and a further 12 items (subdivided into four subsections) for measuring motivation according to self-determination theory. In contrast to our hypotheses based on constructivist theories, open tasks were less successful for gaining knowledge and less intrinsically motivating. (Contains 4 figures.)