Understanding One: Challenges in Children’s Understanding of Units

This lecture focuses on children’s understanding of units from early counting to more advanced concepts involving measurement and composite units. It reviews research on how children construct the idea of “one” as both a countable entity and a unit that can be iterated and nested within higher-order structures. Common difficulties are examined, including treating collections of units as wholes, coordinating multiple units, and understanding number as a structure of embedded units. Together, these perspectives provide a nuanced account of why unit concepts are persistently challenging.