Alex’s parents describe her as ‘low-functioning,’ whereas John’s describe him as ‘high-functioning.’ But these labels can be misleading.

“Parents often ask around the time of diagnosis, ‘Where on the spectrum is my child; is he at the high or low end?’” says Tony Charman, professor of clinical child psychology at King’s College London. “You sort of do know what they’re asking, but you don’t [really know]. Are they asking about ‘autism severity’? Are they asking about functioning or everyday adaptation?”

Despite her difficulties with language and cognition, for example, Alex does just fine with many parts of everyday life. Most weekdays, she goes to a school for children with autism or other special needs. As soon as she gets home each day, she darts up the stairs to her room and quickly changes into play clothes without any help. She keeps her room neat and organized. Dozens of her original drawings cover the walls of her bedroom. She rattles off the full names of her favorite composers: Wolfgang Amadeus Mozart, Johann Sebastian Bach and Ludwig van Beethoven. When she senses that her younger brother is hurt, she rushes to his side, carrying a makeshift doctor’s kit to try to fix whatever ails him.

Alex often leads the other children in her class in their dance routines, and her mother, Wendy Garish, boasts that a teacher calls Alex one of the best dancers in the class. Alex has even forged friendships with a few others in her class, and has lunch every Wednesday with a boy she particularly likes. “They love each other,” Wendy says. “When they walk together, she grabs his hand.”

By contrast, although John does well in school and excels at many aspects of daily life, he seems to struggle in ways that are not immediately obvious. He has no friends and has trouble interpreting other people’s facial expressions and recognizing emotions from the tone of a person’s voice. During gym class, he walks the lines of the gymnasium floor rather than playing games with others. He can be inflexible, one of the hallmarks of autism. For example, he wears only a certain colored shirt on each day of the week: blue on Mondays and orange on Fridays. But his school requires students to wear only black and white, a policy that at first caused him tremendous anxiety. Until he got used to the rule, John would cope by wearing his colored shirt underneath his black-and-white uniform, which he peeled off as soon as he got home.

It’s clear that Alex and John each function well in certain areas of life and struggle in others; each has an idiosyncratic patchwork of skills and challenges. Their stories illustrate a problem that has plagued autism research for decades: What, exactly, do the terms high- and low-functioning mean and to whom do they apply?

An ongoing study in Canada may be able to help answer this question. Since 2004, a team of researchers at five universities has been tracking more than 400 children with autism, including Alex and John, since they received their autism diagnoses. They are characterizing the children by their developmental trajectories—how their symptoms and abilities in multiple domains change over years and even decades. The long-term study may help explain why these two children diverged in their skills despite starting out with similar ones at the time of diagnosis. It may also explain how the traditional labels need to evolve to accurately describe children with autism.