For 400 years, we were wrong. We believed that our brains were hard-wired. We believed that brains that were injured remained that way. We believed that if we just didn't "get" math, or reading, or whatever, that was just the way we were wired and we never would "get it". We were taught that about our own brains and we based our way of teaching children on that idea.
Over the past 20 years or so, we have learned that we have been mistaken. Our brains are, in fact, changeable. Scientists call this neuroplasticity--neuro, meaning involving the brain, and plasticity, meaning the ability to be shaped or molded. So our brains can be shaped or molded. And we're not even just talking about the wiring of the brain; we are talking about the actual structure of the brain that can be changed.
So, what is it that shapes the brain? It is the experiences we have throughout our lives. EVERY experience we have helps to shape our brains. For me, as a teacher, that is an awesome, yet very humbling concept. Every single thing that I do or say around my students has an impact on them. I have the opportunity to help shape the very brains of my students; to help them not just compensate for, but actually overcome some learning challenges. However, a brain that is changeable is also vulnerable. If I misspeak, am just not "on top of my game" one day, or heaven help me, speak in less than a kind manner to a student, I am also shaping that student's brain, but in a negative way. As Voltaire said (and Peter Parker's Uncle Ben in Spiderman), "With great power comes great responsibility".
With the understanding that a person's brain is structured according to that person's experiences, the task of a teacher is much more clear. Appropriate interventions, especially early interventions, do result in measurable changes in students' brains. Therefore, we must provide our students with a multitude of rich experiences, particularly if the students come from environments in which those experiences were not provided. The challenge, and therefore our professional expertise, comes in determining which students need which experiences and planning appropriate activities to provide those experiences. In doing that well, we can have an impact on our students that previous generations never dreamed was possible.