Life is a school; we never stop learning. The 12-20 years that we spend in a classroom are only part of the learning process that begins the moment we are born and ends when we die. And to some, who believe in a life after death, our learning continues on indefinitely.
According to the http://www.thefreedictionary.com/school, the definition of the verb "to school" is
To train or discipline; to educate in or as if in an institution of learning.
And from http://dictionary.reference.com/browse/learning, learning is defined as
the act or process of acquiring knowledge or skill.
That being the case, our schooling begins the second we draw our first breath of life as a tiny, newborn infant. From Day 1 in this life, we are being taught. By the time we are old enough to go to an institution of learning, we will already have 5-6 years learning experience. Picture those 5-6 years in your mind. Picture the tremendous progress from helpless babe in arms, that can only communciate through crying and has to have everything done for them to the chattering, active, independent boy or girl our baby has grown into. Not only has the body increased in size, but the brain capacity has multiplied astronomically. In five short years, your child has learned to talk, walk, and reason.
At age five or six, we send our children off to school where they remain for about twelve years, ultimately graduating from high school at about age eighteen. Many go on to higher institutions for 2, 4, 6, or 8 years, getting rewarded with college degrees in preparation for their chosen careers. That is the importance of schools-to help prepare us to better live our lives. But does the learning stop there? It does not.
Throughout our lives we are constantly learning new things and will never stop learning new things. Our formal years of schooling may be over with, but the learning continues on until we die.