This study explored 30 Grade 1 to 6 (6-12 years old) Thai students' existing ideas about energy. The study employed the Interview about Event (IAE) approach. During IAE, the cards of an event or things were showed to students in order to probe their views of energy concepts. Findings indicated that young students held various alternative conceptions about energy that could be categorized into five different groups relating to electric energy, potential energy, mechanical energy and forces, heat energy, and fuel. Most of Grade 1 to 3 students considered energy as mainly mechanical energy and forces, or electric energy, while the majority of Grade 4 to 6 students clarified their ideas about energy by referring to potential and electric energy. The paper discusses the findings and their implications for teaching and learning with reference to a teaching unit that was developed and evaluated using Thai primary school students.