By utilizing inquiry processes, such as observing and questioning, young children learn to investigate and use evidence to evaluate information. Through intersubjectivity, or social collaboration and mutual focus, children coconstruct an understanding of the world. Children's inquiry and intersubjectivity were observed in a range of activities in this case study over a 5-month period at a preschool in the United States. The role of teacher guidance and the influences of a mixed-age grouping were also investigated. Although younger and older children were equally likely to engage in the basic inquiry processes of observing and questioning, analyses confirmed that older children were more likely to use advanced inquiry processes, such as planning and evaluating. Teacher guidance techniques of inquiry-based guidance, directing attention, and articulating goals were significantly associated with levels of children's engagement in inquiry. Reciprocal conversation among peers was most frequently observed during construction events. The relationship between intersubjectivity and inquiry can be seen through children's collaborative participation and coconstruction of meaning with supportive teacher guidance. The results of this study suggest that activity context, age, and teacher guidance influence inquiry-based learning and intersubjectivity. (author abstract)