In the last century, Jean Piaget proposed one of the most famous theories regarding cognitive development in children. Piaget proposed four cognitive developmental stages for children, including sensorimotor, preoperational, concrete operational, and the formal operational stage. Although Piaget's theories have had a great impact on developmental psychology, his notions have not been fully accepted without critique. Piaget's theory has some shortcomings, including overestimating the ability of adolescence and underestimating infant's capacity. Piaget also neglected cultural and social interaction factors in the development of children's cognition and thinking ability. Moreover, in terms of the methodological approach, Piaget's theory had some ethical and bias problems as he studied his own children. However, Piaget contributions, particularly in regards to the process of education among children and transferring cognition into psychology, have had a significant effect on the science of child development.