Criticisms of Piaget's theory 1. The theory might have underestimated young children's cognitive development. For example, some studies suggest that children show some conservation and some aspects of formal operational thought earlier than Piaget's findings suggest. 2. There is little emphasis on individual differences in development. Also, there has been some debate about the organization of development into stages with the consideration of "mixing" stages. 3. Piaget's stages generally do take place in the sequence that he has outlined. However, the timetable that children follow (i.e., stage change coinciding with age) varies considerably across cultures.