Scientific argumentation is a valid and effective way to involve students in voicing their opinions based on evidence. It helps in the development of scientific thinking and provides opportunities for students to ask more questions. But, just turning students loose and allowing them to argue is not a valid path to deeper understanding. A scientific argument must persuade others that the information (data) and arguments are strong enough to support the theory, model, or proposed action. This month our authors show you how to create classroom environments for assuring valuable argumentation, beginning with very young children.