A three-year-old child in an early childhood class has recently become fascinated by a set of nesting cups in a variety of bright colors. After spending time every day inserting various cups into one another, dumping them out again, and then rearranging them in different orders, the child discovers how to nest them so that all the cups fit nearly together into a single stack. This activity is building a foundation primarily for the child's understanding of which of the following mathematical concepts?

• A. Seriation
• B. Measurement
• C. Symmetry
• D. Probability

Answer: (A)

Seriation is the main concept here. The child is exploring size relationships by comparing cups and figuring out which are larger and which are smaller so they can nest all of them into one stack. This builds an early sense of ordering objects by size, a foundational skill that underpins sequencing and later measurement concepts. The activity isn’t about measuring with units, nor about symmetry or likelihood of events, which is why those other ideas don’t fit as well.