The habit of looking for patterns, the skills to find them, and the expectation that patterns have explanations is an essential mathematical habit of mind for young children (Goldenberg, Shteingold, & Feurzeig 2003, 23). Work with patterns leads to the ability to form generalizations, the bedrock of algebraic thinking, and teachers must nurture this skill in children in the early childhood years (NCTM 2000; NAEYC & NCTM 2002). In this article, the authors look at children's mathematical investigations of patterns inspired by the book "One Is a Snail, Ten Is a Crab," by April Pulley Sayre and Jeff Sayre. They describe how the children in a second and third grade mixed-age classroom used talk, writing, drawing, and gestures to represent their growing understanding of numerical patterns (Dacey & Eston 1999; Trafton & Thiessen 1999; Whitin & Whitin 2000).