How can a teacher improve a child’s brain activity?

PLEASE ANSWER BOTH SEPARTLY
PART ONE- Answer the following questions:
How much of a child’s brain is developed by age 5?
At what age is a child’s brain fully developed?
How can a teacher improve a child’s brain activity?
VIDEO–> Center on the Developing Child at Harvard University. (2013, October 31). InBrief: The Science of Neglect [Video]. YouTube. https://www.youtube.com/watch?v=bF3j5UVCSCA
VIDEO–> Bernard van Leer Foundation. (2012, July 17). Brain development of young children [Video]. YouTube. https://www.youtube.com/watch?v=EFbnU_O9ZEM
PART TWO- Why are there different theories of cognitive development? Why don’t researchers agree on which theory is the right one?
VIDEO—> the simple life channel. (2017, May 17). Piaget and Vygotsky | Early Childhood Development Theories | cognitive development [Video]. YouTube. https://www.youtube.com/watch?v=LdSZV0Knwiw