In this video clip, Kaia and Lincoln agree to begin sorting a collection of donated materials by separating out the glass pebbles, which the children refer to as marbles. The children initially have different ideas about how to sort the pebbles. Kaia works to establish one-to-one correspondence by placing one pebble per compartment in the tray. Alternately, Lincoln wants to group the similarly sized pebbles together in a single large compartment in the tray.