The Decanomial Squares (C218-1) provide a concrete, hands-on representation of the algebraic concept that (1+2+3+4+5+6+7+8+9+10)² equals the sum of the squares of those numbers, bridging arithmetic and early algebra for upper elementary students. This material follows naturally from work with the Bead Chains and supports the passage to abstraction in mathematics by making the relationships between squares and their multiples visually and physically explicit. It's an essential material for any 9–12 environment where students are ready to explore squaring, the decanomial, and the foundations of algebraic reasoning.