Preschoolers' questions may play an important role in cognitive development. When children encounter a problem with their current knowledge state (a gap in their knowledge, some ambiguity they do not know how to resolve, some inconsistency they have detected), asking a question allows them to get targeted information exactly when they need it. This information is available to them when they are particularly receptive to it, and because it comes as the result of their own disequilibrium, it may have depth of processing benefits. In that questions allow children to get information they need to move their knowledge structures closer to adult-like states, the ability to ask questions to gather needed information constitutes an efficient mechanism for cognitive development (referred to in this paper as the Information Requesting Mechanism [IRM]; this term is used because it includes question-asking and other information recruiting behaviors such as gestures, expressions, and vocalizations). However, the role of children's questions in their cognitive development has been largely overlooked. If questions are a force in cognitive development, the following must be true: (1) children must actually ask questions that gather information; (2) children must receive informative answers to their questions if they are able to be of use to cognitive development; (3) children must be motivated to get the information they request, rather than asking questions for other purposes such as attention; (4) the questions children ask must be relevant and of potential use to their cognitive development; (5) we must see evidence that children's questions help them in some way-that is, that they can ask questions for a purpose, and use the information they receive purposefully to successfully achieve some change of knowledge state. This monograph reports data on these points. Study 1 analyzed questions taken from four children's transcripts in the CHILDES database (age 1;2-5;1). This methodology allowed detailed, veridical analysis of every question asked by the children during their recording sessions. Results indicate that children ask many information-seeking questions and get informative answers. When they do not get an informative response, they keep asking; attention is not enough. Results also indicate that the content of children's questions parallel their conceptual advances, and shift within an exchange and over the course of development to reflect the learning process. So, these data suggest that the components of the IRM are in place and are used by children from very early in development, and the information they seek changes with time. Study 2 asked whether preverbal children who are not yet asking linguistic questions can recruit information via gestures, expressions, and vocalizations, in addition to further investigating the linguistic questions of older children. This study analyzed questions from a cross-sectional diary study, kept by 68 parents of their children's questions (aged 1;0-5;0). Also, this methodology allowed for data collection over a large number of children, a large range of situational contexts, and allows for the collection of low frequency, high-salience events. Results from Study 2 suggest that all of the components of the IRM are in place, and extends these findings down to younger, preverbal children who recruit information using gesture and vocalizations. Study 3 investigated the questions asked in one specific domain, biological knowledge, and examined the impact that different stimulus types have on children's questions. This study gathered data from 112 parent/child dyads (children aged 2, 3, and 4 years) walking through one of three zoos (one with real animals, one with drawings of animals, and one with three-dimensional replicas of animals), looking at the animals together. Results from this study also suggest that all of the components of the IRM are in place from the earliest age, further supporting the findings from Studies 1 and 2. In addition, while children still ask many nonbiological questions about the animals ("what is its name?"), biological information ("how do babies grow their bees?") is requested with much greater frequency in this study, although this need not necessarily be the case. Further, the nature of these questions suggests they may support the building of conceptual structures within the domain of biological knowledge, at a time just before the age when children make important conceptual changes in this area. Further, the type of stimulus materials used has an impact on the questions children ask; children are less likely to ask deep conceptual questions when looking at drawings or replicas of objects than when looking at the real thing. Finally, Study 4 examines the causal relation between children's questions and change in knowledge state by investigating whether or not children can ask questions in order to gain information that allows them to solve a problem. Sixty-seven 4-year-olds were asked to figure out which of two items were hidden in a box. Half of the children were allowed to ask questions to help them figure this out. Despite many ways in which they could fail to use questions correctly, children who were allowed to ask questions were significantly more likely to identify the object hidden in the box, an overt indication of their change in knowledge state. Further, children relied on their existing conceptual information about the objects to help generate disambiguating questions; even though they had a faster "dumb" method of disambiguating the objects via nonconceptual perceptual information ("is it purple?"), they were just as likely to generate questions that tapped into nonvisible conceptual information ("does it purr?"). These results suggest that children are capable of using their existing knowledge structures to generate questions that change their knowledge state in a way that allows them to productively solve a problem; they further suggest that tapping into existing conceptual knowledge to help process a current situation, and use that knowledge to generate appropriate questions, is an integral part of question asking. Together, the results of these four studies support the existence of the IRM as a way for children to learn about the world. Children ask information-seeking questions that are related in topic and structure to their cognitive development. Parents give answers to these questions, but when they do not, the children persist in asking for the information, suggesting that the goal of this behavior is to recruit needed information. The content of these questions shifts within exchanges and over the course of development in ways that reflect concept building. Finally, children generate questions efficiently in order to gather needed information, and then are able to use this information productively; they tap into their existing conceptual knowledge in order to do this. Thus, the ability to ask questions is a powerful tool that allows children to gather information they need in order to learn about the world and solve problems in it. Implications of this model for cognitive development are discussed.