Why is the knowledge of growth and development necessary in the educative process?

The human brain does not emerge from the womb fully formed. Indeed, humans develop more slowly than almost any other animal on Earth. While deer for example can walk a few minutes after being born, humans often take more than a year to do so.

The very slow pace of human brain development has the advantage of expanding our ability to learn, but it also has the disadvantage of making it difficult for us to process certain types of information before we reach the appropriate age.

I think the most important application of this knowledge is in curriculum design for students of various ages.

For example, a proper understanding of human brain development would lead us to put foreign language education very early in the curriculum--preferably in elementary school--because language is one of the first systems to come online and the most fluent speakers of any language are always those who started learning it from a very young age.

Conversely, it would tell us to put off most forms of mathematics education until at least middle school, because the brain is not yet ready to deal with the high levels of abstraction required for algebra and advanced geometry. Of course we can still teach arithmetic and basic geometry, but subjecting fourth graders to algebra is unlikely to help anyone.