The purpose of the study reported in this article was to explore the mathematical discourse in which four dyads engaged while sharing the storybook "One Snowy Night" (Butterworth, 1989) while at home or in other locations (e.g., day care centers). Each dyad consisted of a mother and her four-year-old child. Various discourse patterns were evident, and while there were commonalities across dyads, each pair shared the book in unique ways. In two of the dyads, the mother initiated the mathematical discourse; in the other two, the child did. Size, subitizing, and counting were the most common mathematical concepts that emerged. One dyad attended to a single concept of size, and the other dyads attended to more than one mathematical idea. Some parents scaffolded particular problem-solving strategies; others provided more generic support. Based on our findings, we discuss insights and issues and make suggestions for further research. (Contains 1 table and 4 footnotes.)