This case study addresses the issue of climate change denial among students in their first year of vocational education. It was possible to shake the belief that man-made climate change was not happening, through letting students measure the potential of natural forest vegetation and compare their findings with those gathered by their peers nine years earlier. The comparison revealed that old forests had turned into ecosystems, which were adapted for dryer warmer climates. For education for sustainable development, forest education and biology lessons offer the opportunity to establish a long term project, in which peer-to-peer-learning over generations of students is possible, with a high rate of acceptance of the results generated by the former students.