When planning lessons a few decades ago, it was assumed that students would have no scientific knowledge and that good lesson preparation would only have to decide in which order which new terms should be introduced with which didactic aids. However, subject-didactic surveys show that learners do bring their own ideas to many topics into the classroom, which usually do not coincide with today’s scientific concepts. For this reason, chemistry didactics should empirically determine which ideas exist for which facts, and which teaching is advantageous for their correction.