But NIEER cautions that some of these behaviors are normal at this age.
"Hitting your sister is not aggression," said NIEER co-director Ellen C. Frede. "It's the 'super nanny' stuff that you see. Kids doing things over and over like eating dog food and biting mom and destroying things and being incredibly defiant and outside the pale."
Many teachers, like Butler, worry that some children lack the social skills required to learn.
"The teacher needs support — not always a mental health consultant but good old-fashioned behavior management," said Frede. Some children need a "well-organized curriculum" and others just lack parents who are engaged in their lives.
"Just as parents come in different flavors, so do teachers," said Frede. "Sometimes there is too much structure and the child cannot handle it. Other times, the teacher doesn't have enough organization and loses the confidence and trust of her children, who then act out. Three years old is a challenging period."
Poverty and overcrowded classes exacerbate the behavior problems. "My parents cared more about buying their kids new Nikes than giving them a Kleenex when they had a cold," said Butler, who is now teaching in a another preschool.
Colorado mother Amy Gates, who blogs about parenting on crunchydomesticgoddess.com, said preschool expulsions are "kind of shocking." Her 3-year-old attends a private preschool and has had brushes with bad behavior.
When her daughter pushed another child to grab a toy, the teacher used "gentle discipline" to curb any budding aggression.
"There is going to be some acting out in the classroom, especially with preschoolers because they are just learning their boundaries and learning what's acceptable or not," she said.
Andi Silverman, author of "Mama Knows Breast" and contributor to the New York City Moms Blog, said she worries more about accidents in her 3-year-old son's classroom than aggression.
"Expelling a child from preschool is a very harsh measure," she said. "Hopefully, parents and teacher work together."
In New York City, where getting into exclusive preschools is as hard as getting a fat acceptance letter from Harvard, parents and children are screened carefully before they are admitted, according to Silverman.
Most of the nation's preschools are run privately and are not obligated to serve a difficult child, said Karen Hill Scott, a Los Angeles development psychologist and researcher.
"If the child is a problem, they don't have to support them," said Scott. "Public schools have to figure out a way to manage them."
The rise in socially aggressive children is a "warning sign" that reflects directly on parenting, according to Scott.
"There is an inadequate emphasis on self-regulation and self-control," according to Scott, who said adults with low impulse control are less successful in work and in human relations.
Parents confuse "indulgence with love," said Scott. "The helicopter parent hovers, and kids don't learn to fend on their own. The indulged kids never delay any gratification. When everything goes your way, you have a hard time working in groups."
With more children in preschool, the behaviors that once played out in first grade now emerge "in the toddler room," she said.