Contrary to what some might think, babies’ brains are not fully formed little sponges waiting for someone to pour information into them. Babies brains are built during the earliest years through very specific kinds of interactions.
Babies are born with about 100 billion neurons that are the building blocks of the nervous system. Neurons connect to one another through synapses that carry electrochemical signals in response to stimuli, creating pathways that eventually become the “roads” information travels along to all parts of the brain.
'Serve and Return'
The synapses are created through very specific “serve-and-return” 
interactions. Think of a tennis ball with two players on a tennis court. One hits the ball to the other, who hits it back, and as they play, the ball goes back and forth over the net. Brains are built in much the same way. For example, Mom, Dad or an early childhood professional might say something to the child, which is like “serving” the ball across the court, and the baby “returns” it by answering. Even though they’re not technically talking, a baby’s brain is going back and forth, and that is what’s actually building brain architecture.
Building babies’ brains is a lot like building a road using serve-and-return interactions. When a synapse connects, it’s not very strong and the brain is like a dirt road. As the child has more serve-and-return interactions, the dirt road becomes a gravel road and then a paved road and a highway and then a superhighway. The only way it becomes a stronger road that allows faster travel is if the child is using that part of the brain and engaging in serve-and-return interactions.
Think about a third-grader sitting at his school desk trying to do a math worksheet. The teacher might say, “We’re going to spend twenty minutes on this math assignment,” and the boy is sitting there trying to do the math, but he can’t quite get it and begins looking out the window or fidgeting with things at his desk. That behavior might be interpreted as not trying hard enough, or purposefully not focusing. But it could be that the parts of his brain needed to do the math are like a dirt road or a gravel road.
If we were to leave Lincoln and drive to Omaha, the fastest way to get there is to jump on the Interstate. It’s not the only way to get there, but it’s the most efficient way. And maybe we could make it even more efficient by getting into a Ferrari or another car that can travel at high rates of speed. But the student doing the worksheet might not have a Ferrari and he might not have a superhighway. If he’s only got a gravel road, he can still get there, but it will take longer and be a rougher trip. He has to go slower on a gravel road, not because he isn’t trying hard enough, but because he doesn’t have superhighway skills. His brain didn’t grow from a dirt road to a gravel road to a paved road to a highway to a superhighway. Children in these situations are as focused as their neural circuitry allows them to be.
Weak Synapses Fade Away
The best way to get from a dirt road to a superhighway is during the first three years when the brain has the most plasticity. It can be done later to some extent—but with lots of extra effort. Synapses that aren’t strengthened and reinforced by serve-and-return interactions fade away through “pruning.” The remaining synapses form the long-term neural foundation for cognitive, social and emotional growth.
