Jean Piaget (1896-1980) was a renowned psychologist of the 20th century and a pioneer in developmental child psychology.He classi?ed the child's development into four sequential periods: (1) The sensorimotor period frombirth through the ?rst 18 to 24
months, (2) the pre-operations period between the ages of two and seven years old, (3) the concrete operations period between the ages seven and 11 years old,
and (4) the formal operations period that begins around age 11 and continues through adolescence