Lisa Gatzke-Kopp and Mark Greenberg of Pennsylvania State University said aggressive responses to being frustrated are a normal part of early childhood, but children are increasingly expected to manage their emotions and control their behavior when they enter school.
The researchers asked all kindergarten teachers in the 10 elementary schools in Pennsylvania's Harrisburg School District to rate the aggressive behaviors of their students on a six-point scale with items such as "gets in many fights" and "cruelty, bullying or meanness to others."
The research team recruited a group of 207 high-risk children and a group of 132 low-risk children to undergo a range of neurobiological measures aimed at understanding how aggressive children experience and manage emotions differently than their non-aggressive classmates.
The team assessed all of the children's cognitive and academic skills using standardized tests that identified the children's developmental level of vocabulary, spatial reasoning and memory.
The first group of kids was characterized by lower verbal ability, lower levels of cognitive functioning and fewer executive function skills. These children needed verbal skills to understand the feelings of others and guidance from adults to express feelings without hitting.
The second group of kids had good verbal and cognitive functioning, but they were more physiologically aroused, were more emotionally reactive and tended to have more stressors -- they can communicate, but act on impulse.
The findings were published in Development and Psychopathology.