Although electromagnetic radiation is an omnipresent phenomenon in our everyday life, in Austria it is only taught in high schools. Our aim is to develop a research-based teaching and learning sequence on electromagnetic radiation for the middle school level. As a first design step, we developed central explanations, so called key ideas, to introduce the term of electromagnetic radiation and the interaction with matter. Those key ideas were evaluated with teaching experiments, using the method of probing acceptance. The outcomes are encouraging and help us to get a better understanding of students' problems and their perspectives while learning about radiation. The key ideas were adapted accordingly.