Environmental education in school lessons makes a central contribution toward implementing the United Nations' requirement of sustainable development. In science lessons, various ecosystems can be examined to illustrate the consequences of anthropogenic influences on our environment. One important ecosystem is the UNESCO World Heritage Wadden Sea. This has not been considered in science education research so far. The present study determines the effects of environmental education on the Wadden Sea on environmental psychological constructs. Therefore, 157 students (age: M = 14.4 years, SD = 0.5) were tested in a pre-post design with a subsequent follow-up test to determine changes in connectedness with nature and environmental attitudes as a result of the lessons. The Inclusion of Nature in Self Scale was used to elicit nature connectedness, and environmental attitudes were based on the Two Major Environmental Values model. For the statistical analysis of the data, a one-factor analysis of variance with repeated measures was performed in each case. Statistically significant short-term and long-term positive effects of the educational intervention on students' environmental attitudes and connectedness with nature were found. Thematizing the Wadden Sea in school lessons was found to promote the corresponding attitudes in the short term and long term.