Rocks. Jewels. Shells. Keys. Collections. All children have them – just ask. Remember dumping out a box of buttons or shells and putting them into categories? Then perhaps you named each set. In order to do this you had to identify some kind of attribute of each group – an attribute describes a property that some things have in common. Exploring these collections helps children to observe similarities and differences, compare objects by attributes such as color, size, shape, develop language skills, and connect their observations of attributes to other real world experiences. Understanding that objects can belong to more than one category helps children to develop flexible thinking. Asking children to name the categories and describe attributes supports vocabulary development. Eventually, as children sort and classify, they naturally move to counting or patterns, making sorting a foundational part of children’s math learning.