Jean Piaget

One of the biggest names in music education is Jean Piaget.  Piaget developed the idea that there are four stages that kids go through in the learning process.

1. Sensorimotor- This stage occurs between the ages of one and two, and it is learning through direct sensory experience, or touching things.
2. Preoperational- This stage is between the ages of two and seven and it is learning through the manipulation of objects, learning consequences to actions, and therefore translating stimuli into symbols.  At this point, they don't quite understand the logic behind why things happen, all they know is that certain things happen as a result of their actions.
3. Concrete operations- From ages seven to eleven, children start viewing objects in a more concrete tangible way, but not yet abstractly.  They begin understanding systematic ways that things happen.
4. Formal Operations- From age eleven on, children begin to learn abstractly using logic and deductive reasoning.  This final stage describes how we think today as adults as well.

These four stages are essential to teaching children and deciding what and how to teach them certain material.  For instance, when teaching music to a two year old, you just want to expose them to some form of music and get them listening in dancing.  It would be very hard to teach a child how to read music until they were at least seven, because that's when they start recognizing symbols.