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It’s back-to-school season. Parents mark their youngsters' height on the wall and marvel at how much they’ve grown, but what’s going on just below the pencil line in that child’s brain?

We know brain development continues from infancy to adulthood, but many parents underestimate how much a child’s brain changes from year to year and how those changes can influence behavior.

Decades of scientific studies have shown even an immature brain is capable of extraordinary feats. Yet a fully developed brain is necessary for actions that adults take for granted, such as risk assessment and self-control. According to developmental psychologists, parents who better understand the stages along the way can help guide their child over the hurdles.

Babies are surprisingly good at communicating

Babies are looking, listening and imitating from the time they are born. Stick your tongue out at a baby, even one just hours old, and he or she may do the same back at you, said Sarah Lytle of the Institute for Learning and Brain Sciences at the University of Washington.

Yet many parents don’t realize how quickly infants begin to develop social and emotional awareness, said Ross Thompson, who is president of the child development organization Zero to Three and a cognitive psychologist at the University of California at Davis. “Parents underestimate how sensitive a child is to their own emotions,” he said. As early as 6 months of age, a child can be affected by a parent’s depression or anxiety and by marital squabbles.

Babies also look to their parents for guidance in uncertain situations. If you’re on a subway and start interacting with the little one next to you, the baby may turn to the parent to see how to respond to you. This process is called “social cognition” or “social referencing,” and it’s not very different from when adults at a party wait to respond to a joke when they’re unsure whether others will find it funny or offensive.

To help infants learn, parents should frequently look at what they’re talking about and change their gaze slowly, Lytle suggested. This important social cue helps with language development, she said — with babies who follow gazes closely having a more diverse vocabulary by the time they’re 2.

All languages sound the same initially to a newborn, and then a tuning process begins. By about 10 months, babies start to specialize in the language they’re used to hearing. It’s important to talk to your child during the first year, especially using “parentese,” Lytle said. This infant-directed speech is not “baby-talking,” despite its typical singsong tone and repetition, but uses real words in grammatically complete sentences.

While we typically underestimate babies' ability to understand and communicate before they begin speaking, we tend to overestimate the brain power of walking, talking toddlers.

Toddlers are mentally incapable of sharing and self-control

In a survey conducted by Zero to Three in 2015, nearly half of parents believed their children could learn to share by the time they are 2. But according to the cognitive psychologists at Zero to Three, this skill does not typically develop until a child is 3 or 4. That may be because they haven’t yet developed what’s known as “theory of mind.”

Theory of mind is the ability to differentiate one’s own perspective and preferences from someone else’s. A classic experiment in theory of mind is known as the Sally-Anne test, in which a child is told Sally has a basket and Anne has a box. Sally puts an object in her basket, then leaves. While Sally is gone, Anne moves the object to the box.

The child is then asked where Sally will look for the object when she returns. Correctly answering that Sally will look in her basket signals the child understands they have a perspective that is different from Sally's.

Theory of mind is important for developing empathy, making friends and even doing well academically, Lytle said. Parents can help their children develop perspective by talking them through scenarios like the Sally-Anne test or reading books that help them to build cognitive parallels, she said. For example, in a book where a character goes to a doctor, they can compare the situation to when the child went to the doctor and discuss how the experiences were similar or different.

According to that 2015 survey, the majority of parents also believed 2-year-olds can control their emotions and impulses. Yet children have very limited self-control abilities until they are about 4. When toddlers won’t stop throwing a fit, do something forbidden or refuse to share, “they’re not being willfully obstinate,” Thompson said. “Many parents overestimate a child’s capacity for self-control.”

Thompson recommends helping young children with self-control — for example, by distracting them with a favorite toy while passing candy in the grocery store checkout aisle. And when dealing with a tantrum, acknowledge a child's feelings by putting them into words. “A lot of their frustration is the feeling of being misunderstood,” he noted.

He also suggests giving the child the impression that they have some control. In his own case, when his young son didn't want to go to bed, Thompson would ask the boy whether he wanted to play for a few more minutes. Yes, a distinguished professor in psychology was on his knees, negotiating with a 3-year-old, but Thompson says parents who understand how their toddlers' brains work (or don’t work) will find it fairly easy to outsmart them. It’s good to tell a child “no” because they’re learning language, he added, but you can’t expect them to change their behaviors.

Teenagers don’t think with the same parts of their brain as adults

For some parents, a seemingly erratic teenager can make those long-ago toddler days seem like a walk in the park. Frances Jensen, neuroscientist at the University of Pennsylvania and co-author of “The Teenage Brain,” suggests understanding how teens think can improve the experience for both sides.

Connections in our brain develop from the back to the front, and those important for higher-order thinking continue to form and strengthen into a person's 20s. “Teenagers have good connectivity up to about their ears,” Jensen explained. And at this age, the midbrain, important for emotion, sexual function, learning and memory, is hyperactive.

As teens transition into adulthood, connections in the front of their brain are strengthened while those in the other regions are pruned. A fully developed frontal lobe is essential for planning, decision-making, impulse control and risk avoidance.

These stages of development showed up in a 2006 imaging experiment. Researchers discovered adults trying to identify fearful facial expressions used more of the front of their brain, while teens used the emotional centers in the midbrain — meaning teens literally think using different parts of their brain.

The finding might explain why some teen behaviors surprise adults. “Teenagers are actually more susceptible to stress,” Jensen said. If your teen comes home distraught because someone made fun of their hair, you might be tempted to say it’s no big deal. But the activity in their brain likely resembles an adult brain's response to news of a major international incident.

The plasticity of teen brains — their ability to lose, form and strengthen connections — also makes adolescents especially susceptible to addiction to everything from video games to cocaine, Jensen said. Activities such as binge drinking and chronic marijuana use can be especially damaging at this age.

Jensen recommends giving teens a “frontal-lobe assist” by helping them to plan, prepare and even rehearse for situations that require higher judgment. Help them develop and learn phrases to use as excuses to avoid making a bad decision amid social pressure, for example. And if they do make a bad decision, she suggests using the situation as a teachable moment instead of lecturing or alienating them.

Throughout a child's life, parents who understand some basics of brain development can adjust their expectations and better come up with strategies to prevent frustration for everyone. In other words, a little understanding goes a long way.

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