School was difficult for Makayla Caliendo when she was young. She remembers staring out the window while her classmates were paying attention in class. Some clothes, tags and socks were uncomfortable and left her unable to focus. She even had to repeat preschool.

“I left those early school years with less knowledge than my peers,” Caliendo wrote as a high-school senior in Attention magazine. That was back in 2021. Those experiences had “made me feel dumb.”

Scientists Say: Neurodivergent

But Caliendo wasn’t — and isn’t — dumb. Her brain just works differently than most of her peers.

Caliendo has a condition known as attention deficit/hyperactivity disorder, or ADHD. It affects how people think, learn and process information. Although sometimes called a “disorder,” ADHD is actually a neurotype. That means it’s a natural — and fairly common — variation in how the brain develops.

Some 22 million people in the United States have been diagnosed with ADHD. This includes more than 6 million children.

People with ADHD produce a lower amount of some of the chemicals that brain cells use to communicate. One is dopamine. It affects motivation and mood. Another is norepinephrine (Nor-ep-ih-NEF-rin). It plays a role in attention and excitement.

Explainer: What is dopamine?

These brain differences can make it harder for people with ADHD to focus on certain tasks when compared to folks without ADHD. People with ADHD may have trouble sitting still or controlling their emotions and actions.

Such traits are not always a problem, notes Jamal Williams at the University of Buffalo in New York. He studies the genetics behind ADHD. People have had traits linked to ADHD for a very long time. Recent research suggests ADHD-like behaviors, such as risk-taking and impulsivity, would have made people better foragers in ancient hunter-gatherer societies.

However, people today are expected to sit still in classes and offices. They may have to be quiet for hours at a time. This can make it difficult for people with ADHD to succeed in such environments.