This chapter presents event diagrams as a representational tool that allows students to visualize relativistic phenomena. It puts particular emphasis on thought experiments that can help students obtain a deeper understanding of physical phenomena that are hard to imagine. The chapter is intended for readers who look for instructional models to teach concepts of special relativity at the secondary school level, and also, for those who wish to learn more about thought experiments as instructional tools. Students perform the thought experiment by drawing light propagation in the event diagram. Compared to the traditional presentation of thought experiments, the event diagram stimulates students to reason with light propagation more explicitly. Like all external representations, event diagrams are a simplified and idealized display of reality and are inherently limited. To wrap up, the authors have shown how their tasks stimulate students to perform thought experiments by drawing light propagation in event diagrams.