Piaget observed among his children, that as infants they all manipulated objects as a way in which to gain knowledge about them. By touching, looking, and sucking on objects, they were able to learn about them. He called this the sensorimotor stage of intellectual development, lasting from birth to two years old, because intelligence at that time is measured largely by the infant's deliberate motor actions, and the immediate sensory feedback they receive from those actions.
Piaget characterized the years from two to seven, as belonging to the period of preoperational thought. Children can now think about absent objects, and often make up new symbols or objects to represent others, such as a stick of wood being transformed into a ray gun. They can understand the stable, identifying features of an object, but have trouble comprehending when that same object is in some manner transformed.
According to Piaget, when children are about seven or eight years old they develop the ability to understand reversible actions called "operations". This means that they understand that if you roll a ball of clay into a sausage shape, you can reverse this action and turn it back into a ball of clay. Although the child is becoming capable of increasingly logical thought, he or she still has trouble dealing with abstract ideas.
By about the age of twelve the child should be entering the last stage, known as the period of formal-operational thought. Now the child can apply operational thinking even to actions that are not reversible in actuality, but in theory.
There are three basic strengths of Piaget's theory in the preceding section. The first is the order and structure derived from the theory's types of knowledge, stages of knowledge development, and processes of knowledge development. A second strength is the guidance it gives to teachers in determining student stages of knowledge and how to help students move to higher stages. A third strength is the general nature of the theory and the three guiding principles as outlined above.
One of the weaknesses is that the model is flawed and is not always 100% accurate, it is at best a way to guesstimate. Another weakness is that scientist now believe that each learning facility operates on a different level(modularity of mind) unlike Piaget's belief that they were intertwined
The key ideas of Piaget's and Vygotsky's theory differ. Piaget believed that intelligence came from action. He held that children learn through interacting with their surroundings and that learning takes place after development. Alternatively, Vygotsky felt that learning happens before development can occur and that children learn because of history and symbolism (Slavin, 2003, p.30, 43). Vygotsky also believed that children value input from their surroundings and from others. Piaget did not place importance on the input of others. Piaget and Vygotsky's theories on cognitive development also have differing opinions.