According to Piaget, cognitive development involves a reconstruction of the world, where more and more complex structures develop around experience-bound simple schemas. Piaget’s cognitive developmental theory focuses not on the obtaining of information, but on the development of abilities. He distinguishes between separate stages of development, and also describes the processes which allow transitions from one stage to the next (equilibrium, accommodation and assimilation). In his theory, the four stages of development are the sensorimotor, preoperational, concrete operational and formal operational stages.