1. Schemas
   1. a mental structure that represents some aspect of the world
2. Adaptation
   1. What it says: adapting to the world through assimilation and accommodation
3. Assimilation
   1. The process by which a person takes material into their mind from the environment, which may mean changing the evidence of their senses to make it fit.
4. Accommodation
   1. The difference made to one's mind or concepts by the process of assimilation. Note that assimilation and accommodation go together: you can't have one without the other.
5. Classification
   1. The ability to group objects together on the basis of common features.
6. Class Inclusion
   1. The understanding, more advanced than simple classification, that some classes or sets of objects are also subsets of a larger class. (E.g. there is a class of objects called dogs. There is also a class called animals. But all dogs are also animals, so the class of animals includes that of dogs)
7. Conservation
   1. The realisation that objects or sets of objects stay the same even when they are changed about or made to look different.
8. Decentration
   1. The ability to move away from one system of classification to another one as appropriate.
9. Egocentrism
   1. The belief that you are the centre of the universe and everything revolves around you: the corresponding inability to see the world as someone else does and adapt to it. Not moral "selfishness", just an early stage of psychological development.
10. Operation
    1. The process of working something out in your head. Young children (in the sensorimotor and preoperational stages) have to act, and try things out in the real world, to work things out (like count on fingers): older children and adults can do more in their heads.
11. Schema (or scheme)
    1. The representation in the mind of a set of perceptions, ideas, and/or actions, which go together.
12. Stage
    1. A period in a child's development in which he or she is capable of understanding s ome things but not others