It is important to consider each of Piaget’s stages individually as there are some who support and others who reject his ideas. The first stage in his model is the sensori-motor stage which lasts from birth to about 2 years old. The key achievements of this stage are object permanence (an awareness that objects continue to exist even if cannot be seen), and imitation. There is evidence that infants show partial object permanence, Piaget attributed this down to the child not remembering where the object has been hidden. However one study showed that 8 month old infants were surprised when a toy was lifted from behind the “wrong” screen after being placed behind another. This indicated that they did remember where it had been put.
The second of Piaget’s stages is the pre-operational stage- in this children focus on only one aspect of the situation (centration) and so don’t show conservation. Their thinking is characterised by egocentrism, the sense of being the centre of everything and that their view is the only view, this stage occurs between 2-7 years old. However, this is challenged by Wheldall and Poborca (1980) who argue that children possess more knowledge of conservation than seemed to be the case in Piaget’s liquid conservation studies. They claim children often fail on the task because they don’t fully understand the question; accordingly they created their own non-verbal test and found 50% of children showed conservation.
Piaget studied egocentrism in the pre-operational stage by using the three mountains task. Children were shown a model from one angle, then shown photographs from other viewpoints, and asked to choose which view someone standing at the other labelled points would see. Pre-operational children usually selected the view from the point at which they were looking themselves. According to Piaget, this error occurred because young children can’t escape from an egocentric perspective. However Hughes argued children in fact performed poorly because the task doesn’t relate to their experience. He constructed his own version of the experiment which involved a boy doll and two policemen dolls, and found that 90% of children tested performed the task successfully. This suggests that Piaget’s initial study was flawed in its design; therefore this stage of his model severely lacks validity. The main reason for the difference is probably that Hughes’ task was much more meaningful and interesting, it was also simpler that the one used by Piaget.
The third stage is known as the concrete-operational stage, 7-11 years, this is when children show an increasing independence of thought from perception. This is associated with the development of conservation, reversibility, and an understanding of mathematical functions. One of the achievements of this stage is transitivity, which allows three of more elements to be placed in the correct order. According to Piaget children less than 7 years old shouldn’t show transitivity, however Pears and Bryant (1990) found evidence of transitivity in 4 year olds. This would imply that children make transitive inferences several years earlier than assumed by Piaget.
The final stage of Piaget’s cognitive development model is the formal operations stage, occurring from 11 years old upwards. Adolescents can think logically about abstract ideas or potential events. He suggests children and adults in this stage have the ability to think in terms of many possible states of the world. Although, it has been argued that Piaget greatly overestimated the intellectual capability of most adolescents. Bradmetz (1999) assessed formal operational thinking in 62 15-year olds using various Piagetian tasks. Only one participant showed substantial evidence of formal operational thought. Bradmetz also found that overall performance on the tests of formal thought correlated +.61 with general intelligence. Therefore, the cognitive abilities associated with formal thought resemble those assessed by traditional intelligence tests.
General criticisms of Piaget’s theory surround his use of methodology. He was fond of using case studies, where an individual was studied in great depth. This provides rich information about that particular child but is very subjective in its content, therefore cannot be generalised to entire population. This is an important point as Piaget claims that every child passes through the same stages, which are based on innate structures and therefore are present in everyone. Furthermore, Piaget often observed the behaviour of children, namely his own. This has obvious methodological setbacks, primarily lacking in representativeness and highly questionable as to be free from bias. On the other hand he sometimes used cross-sectional studies i.e. used groups of children from varying ages and compared them on the same task to judge performance. This could be seen as a positive use of qualitative methods, as performance can be directly compared to variation of age groups, although negative aspects concerning sample size and representation can still apply.