At the botanical garden of the University of Würzburg, we conducted practical lessons on bionics, focused on the lotus effect, with 260 students. Those approx. 14 years old, 8th-grade mid-level students were divided into two groups. During an instructional discussion about the topic, one group was confronted with their alternative conceptions (AC), whereas the other group was not (NAC). Both groups were treated equally, following the experimental phase and results discussion. Questionnaires were used to measure conceptual change in a pre-, post- and retention test design. Both groups changed their conceptions in short-term similarly. Over a long-term period, the NAC group showed significantly higher knowledge than the AC group. We discuss that the methodology of the alternative conception confrontation should be selected very carefully by the teacher, as this step is the most delicate within the whole conceptual change process.