Cognitive development refers to the progression of mental abilities, such as thinking, problem-solving, and learning. Key theorists include Jean Piaget, who proposed stages: Sensorimotor (0-2 years), Preoperational (2-7 years), Concrete Operational (7-11 years), and Formal Operational (12+ years). Lev Vygotsky emphasized the role of social interaction, introducing the concept of the Zone of Proximal Development (ZPD) where learning occurs with guidance