Piaget became fascinated in his early studies with his discovery that children of the same age often gave the same incorrect answers to questions, suggesting that there were consistent, qualitative differences in the nature of reasoning at different ages, not simply a quantitative increase in the amount of intelligence or knowledge. This discovery marked the beginning of Piaget's continuing effort to identify changes in the way children thinkhow they perceive their world in different ways at different points in development. Piaget's contributions can be summarized by grouping them into four main areas. First, he produced literature on the general stages of intellectual development from infancy through adulthood. This concern occupied him from 1925 to 1940, and after 1940 he began to describe some of the developmental stages in formal, structural terms using models from symbolic logic (Flavell, 1963, 1-9).
The different stages postulated by Piaget help to explain different rats of learning at different ages as well as the types of learning possible at different ages for the majority of the population. Learning itself is seen by Piaget as a process of discovery on the part of the individual, and learning as a formal activity becomes a system of organization by which instruction is enhanced by the way the teacher arranges experience. Learning is thus experiential, and Piaget suggests that experiences have meaning to the extent that they can be assimilated. Such assimilation does not take place without accommodation, an aspect of considerable importance from the point of view of adaptation and possible development:
One of the principal aims of the teacher will be to present situations to the child which require him to adapt his past experience. The teacher is concerned with facilitating adaptation and assisting the child along the developmental path (Flavell, 1963, 91).
The learning situation thus becomes a means of discovery as the child encounters something that is unknown, new, or problematical for the child. The achievement of understanding of this experiences produces an adaptation, and each adaptation made by the child is a discovery for him or her, an insight made through experience. Such a discovery process is ongoing and is not to be seen as a series of leaps from one insight to another. The process of discovery continues and builds on experiences already assimilated and adapted. The process "is marked out by minute consolidations and extensions of past experience, with perhaps an occasional flash of insight" (Flavell, 1963, 91-92).
There are two principal learning theories in psychology, one of which focuses on the learning process while the other focuses on the capacity to learn. Piaget offered a biological theory of intelligence that was quite different and that he presented as a unified approach to intelligence and learning. Piaget restricted the ideal of learning to an acquisition of new knowledge that derives primarily from contact with the physical or social environment:
He opposes it on the one hand to maturation which is based on physiological processes; on the other hand and most importantly he differentiates it from the acquisition of general knowledge or intelligence which he defines as the slowly developing sum total of action...