As every parent knows, children are no slouches at generating questions. But the scientific potential in a child's spontaneous question can easily be lost; children often fail to take the step beyond casual curiosity into systematic inquiry. Questioning is indeed robustly rooted in children's everyday ways of thinking about the world, but serious classroom support is required if these children's questions are to become productive guides to scientific inquiry. Similarly, children are apt at generating justifications to support their actions or points of view in an argument. However, they often regard their actions or beliefs as unproblematic, even self-evident. In contrast, scientific inquiry demands a separation between belief and evidence, so that each can be considered apart and their relations made explicit. Thus, question posing and evidence-generating go beyond common sense, and so must be nurtured explicitly in science education.