In this study we explored questioning behaviors among elementary students engaging in inquiry science using the "Knowledge Forum", a computer-supported collaborative learning tool. Adapting the theory of systemic functional linguistics, we developed the Ideational Function of Question (IFQ) analytical framework by means of inductive analysis of the questions found in 10 online forums contributed by three classes of Year 4 elementary school students and their teachers. We found 25 categories of questions which we grouped into three main kinds: Scientific, Epistemological, and Meta-discoursal. We then narrowed our analysis to three forums involving digestive systems. Using the IFQ framework, we explored the relationship between nature of inquiry task and students' questioning behaviors. Our analysis shows that for close-ended task that sought scientific facts from authoritative sources, students tended to ask only scientific questions. For open-ended problem-solving task that demanded epistemic justification from the students, there was more even distribution in all three kinds of questions. (Contains 6 tables.)