By the age of two a toddler is mobile and can use language but still lacks adult reasoning ability.
This means that they display some characteristic errors in reasoning.
Piaget conservation experiment - counters
placed two rows of eight identical counters side by side
young children correctly reasoned that each row of counters had the same number
however, when the counters in one of the rows were pushed closer together, pre-operational children struggled to conserve and usually said there were fewer counters in that row
Piaget conservation experiment - liquid
Piaget found that when two identical container were placed side by side with the contents at the same height, most children spotted that they contained the samevolume of liquid
However, if the liquid was poured into a taller, thinner vessel, younger children typically believed there was more liquid in the taller vessel
Piaget and Inhelder (1956) - egocentrism
Demonstrated in the three mountains task, in which children were shown three model mountains, each with a different feature: a cross, a house or snow
A doll was placed at the side of the model so that it faced the scene from a different angle from the child
The child was asked to choose what the doll would 'see' from a range of pictures
Pre-operational children tended to find this difficult and often chose the picture that matched the scene from their own point of view
Piaget and Inhelder (1964) - class inclusion
Children under the age of seven struggle with the more advanced skill of class inclusion, the idea that classifications have subsets
When 7-8 year old children were shown pictures of five dogs and two cats and asked 'are there more dogs or animals?' children tended to respond that there were more dogs
He interpreted this as meaning that younger children cannot simultaneously see a dog as a member of the dog class and the animal class
