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1. Primary circular reactions
based around coordinating  sensation and new schemas
2. Secondary circular reactions
the child begins to repeat a action to elicit a reaction from the environment
3. Tertiary circular reactions
Trial and error experimentation.

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Kids in this stage start to engage in symbolic play and manipulate symbols, however have no understanding of concrete reasoning. language development is also a hallmark of this stage

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This stage is where the child gains the ability to preform and understand concrete reasoning and starts to understand reversibility.

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This stage is where abstract thought takes off and the person is able to form hypothetical ideas.

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Criticism
the samples are difficult to generalize
Lack of clear operationally defined variables
Support
his theories helped determine that students should be taught at the developmental stage they are at.