Until recently, little was known for certain about how the brain changes as children age and grow. Considerable progress is being made in charting developmental changes in the brain, although much is still unknown. The number and size of the brain's nerve endings continue to grow at least until adolescence. Some of the brain's increase in size also is due to myelination, a process in which many cell of the brain and nervous system are covered with an insulating layer of the fat cells.

This increases the speed at which information travels through the nervous system. Myelination in the areas of the brain related to hand-eye co-ordination is not complete until about four years of age. Myelination in brain areas that are important in focusing attention is not complete until the end of the elementary school years.

The implications for teaching are that the children will have more difficulty focusing their attention and maintaining it for very long in early childhood but their attention will improve as they move through the elementary school years. Even in elementary school and later, many educators believe occasional short breaks sustain children's energy and motivation to learn. Another important aspect of the brain's development at the cellular level is the dramatic increase in connections between neurons (nerve cells).

Synaklpses are tiny gaps between neurons where connections between neurons are made. Researchers have discovered an interesting aspect of synaptic connections. Nearly twice as many of these connections are made than ever will be used. The connections that are used become strengthened and will survive, while the unused ones will be replaced by other pathways or disappear.