A fundamental understanding of sustainability, and connected to this the insight for the urgency of the conservation of nature, requires however, the knowledge of ecological systems and principles. Photosynthesis is the most important biological process in the global ecosystem. Only if students have this ecological insight, they can understand the basis of nutrition of plants, animals and humans and they can understand environmental problems like global warming or uprooting of rain forests. Sustainable Development stands for an education, which enables people to anticipate global problems, to face the problems and to sort them out. There is a need of a basil ecological education as early as possible (Carlson 2002). Photosynthesis play a decisive role in scientific education. But pupils often find them to be difficult to understand. The metabolism of plants appears abstract and complex. So many pupils hold pre-existing conceptions which are not in line with the generally accepted scientific view. There is agreement among education scientists that the adoption of appropriate scientific concepts is a constructive process requiring the active cognitive engagement of individuals. As a consequence learning environments that support constructivist processes create meaningful opportunities, allowing pupils being active as well as discovering new explanations. A typical learning environment of this kind encourages activities like experimentation (Hardy et al. 2006).

Stern and Möller (Staub, Stern 2002; Möller et al. 2003) found out that children in primary school are already able to cope with complex learning processes in mathematical and physical education. But it is not definitely taken that this also applies for ecological topics due to the fact that ecological topics are often not taught by scientific competences like experiments but rather with methods from linguistic education. There is limited research on the influence of experiments to the development and integration of scientific concepts about photosynthesis within children at the entry-level of secondary schools. Previous research focused on the increase of new knowledge rather than on the conceptual change. The results are inconsistent.

The following objectives are in the centre of this study: Do sixth grade pupils in Germany develop adequate and expandable conceptions about photosynthesis when learning in a moderate constructivist environment which attaches importance to experiments rather than pupils learning in a moderate constructivist environment which attaches less importance to experiments?

Are non-performance variables like interest or motivation better promoted in a moderate constructivist learning environment including much experiments than in a moderate constructivist learning environment with few experiments?

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