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But an active nature complicated by attention deficit hyperactivity disorder, ADHD, can make him a handful some days.

For his former preschool, there apparently were too many "some days," which included defying his teacher's instructions and hitting classmates. After just a few months, the school's director called in Joanah's mother.

"They just seemed kind of intolerant," says Lori Napier, of Lakewood, Ohio. "He wasn't a holy terror. Basically, they couldn't handle him -- or didn't want to -- and asked me to remove him."

Yale researcher Walter S. Gilliam says preschool programs exist to ready young children for kindergarten and the elementary years that lay ahead. So expelling a kid so young, even with problem behavior, just doesn't make sense.

"I can't think of a child who's more in need of a school-readiness program," says Gilliam. "It's like taking sick people out of the hospital." More likely than a teen

At the same time, preschoolers were far more likely to be kicked out of school than their counterparts in the K–12 system. The preschool expulsion rate of 6.7 per 1,000 preschool students was more than triple that of older grades.

"It shocks a lot of people," Gilliam says.

The study didn't look into the reasons for expulsions, but anecdotal evidence from preschools points largely to aggressive behavior, including biting and hitting, and other hard-to-control behaviors, such as running away.

"I moved him because I was so unhappy ... but they were very happy when I said we were leaving," she says.

Visits to doctors and clinicians had showed there was nothing abnormal about Wyatt's behavior, Besnoy says. "He wasn't hitting anyone. He wasn't aggressive. He just didn't like being told what to do. He's 3 years old, you know?"

Wyatt didn't like to stay at an academic station like instructed, or sit still for 20 minutes of class time, things Besnoy sees as "unfair demands" for a little kid.

"I think some people have expectations that children that age are able to sit for 20 minutes and listen to a lesson," says Lisa McCabe, associate director and cooperative extension associate of the Cornell Early Childhood Program at Cornell University.

"You stick them in that environment and they start acting out and hitting, and then they're labeled a problem child, when they're not -- you're just expecting things that are inappropriate."

It's natural for a little kid to whack their playmate to get what they want, in part, because it works.

Most young children haven't yet mastered how to "use their words," much less the patience and internal check system to follow through.

A 1996 Canadian study of 2- to 11-year-old children showed that physical aggression peaks between 2 and 3 years of age, and that most kids outgrow the behavior. According to another Canadian study from 2006, only about one-sixth of children, mostly boys from disadvantaged families, show a more persistent pattern of physical aggression.

Biting and hitting are "relatively minor issues," and kids shouldn't be expelled for such behavior, says Beth Green, vice president of the Research and Training Center on Family Support and Children's Mental Health at Portland State University in Oregon.