Which Piagetian substage of sensorimotor development typically occurs latest?

• A. Primary circular reactions
• B. Secondary circular reactions
• C. Tertiary circular reactions
• D. Object permanence

Answer: (C)

Tertiary circular reactions are the latest among the sensorimotor substages. In this period, roughly from 12 to 18 months, infants become curious experimenters, deliberately varying their actions to see different outcomes with objects and the world around them. This marks a move beyond simply repeating actions on their own bodies (primary circular reactions) or on objects in the environment (secondary circular reactions). Object permanence is developing during earlier substages as well, but the most advanced, exploratory behavior listed here is characteristic of tertiary circular reactions.