... they were playing with a toy and it fell out of sight they would not realise it had even existed. Piaget said that the skill of object permanence came at about 9 months. The second stage of CD is the pre-operational stage (2-7yrs), at this stage language is developing but children are unable to conserve (understand that shapes can change without the mass or size having to change) or decentre (can't understand things from another persons point of view). This is also known as the theory of mind. In the concrete operational stage (7-11yrs) children have developed the theory of mind and are also able to conserve if the problem is 'concrete'/visual. The final stage is Formal operational stage (11yrs- onwards). In this stage children are able to work things out abstractly so this is the stage in which children start to be taught algebra. The above ideas about CD were ...

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