This study explores two number composition and decomposition activities from a numeracy perspective. Both activities have the same mathematical structure but each employs different tools and contexts. Twenty kindergarten children engaged individually with these activities. Verbal utterances as well as actions of the child and interviewer were recorded. The children's strategies are described and discussed in terms of how the tools and contexts possibly affected the ways the children employed their mathematical knowledge when engaging with the activities. In addition, children's disposition to use their mathematical knowledge and to use it critically is discussed.