Mary often plays the game peek-a-boo with her baby. Initially, Mary covers her baby and then removes the cover, registering "surprise" at the baby's reappearance. After a time, her baby does the covering and uncovering. This is an example of:

Answer: Scaffolding

Explanation: Scaffolding is the process of learning certain skills, knowledge, mastering tasks, through providing support by someone who is following someone's learning. This can be a parent who monitors the development and learning of their child, a teacher who monitors student learning, etc. It is a systematic process of monitoring and support, by upgrading existing knowledge with new ones, until children have mastered the skills and are able to perform them independently.