GIRLS, traditionally raised to be more passive than boys, are becoming more aggressive, according to a leading author on child behaviour.

Professor James Garbarino, a best-selling author on child aggression and violence, said research showed aggression in girls is increasing.

This may be due to the traditional cultural message that girls are not pushy or violent being diluted by images in the popular media that portray women as aggressive, like Buffy and Lara Croft: Tomb Raider.

"In the past it has been that the clear message has been that girls don’t hit," said Professor Garbarino, who holds the Maude C. Clarke chair in humanistic psychology at the Loyolia University in Chicago.

"However that has changed as we see more girls on TV who hit and are more aggressive generally. Consequently, we are seeing more aggression in girls.

"In many ways we are doing better with boys... but it may be being counteracted with rising levels of aggression in girls."

Professor Garbarino spoke at a national parenting conference run by the Children, Youth and Women’s Health Service in Adelaide yesterday.

He said rates in the U.S. for girls arrested for assault were rising. And studies were showing exposure to violent images was having the same effect on girls as boys, in terms of encouraging violent behaviour.

"Parents can limit their exposure to these violent images," Professor Garbarino said. "They can also show children how to control their aggressive emotions during play."