This article takes the position that teachers can use simple manipulative materials to model relatively complex situations and in doing so scaffold the development of students' number sense and early algebra skills. While students' early experiences are usually dominated by the cardinal aspect of number (i.e., counting the number of items in a set), over time students broaden their understanding to include increasingly abstract concepts, such as negative numbers. The activities described in this article provide a context within which students can investigate number patterns and formulate and test conjectures.