Washington  - More than 200,000 US public school students, often as young as 3 years, were punished by beatings last year, Human Rights Watch and the American Civil Liberties Union said in a report released Wednesday.

Corporal punishment is legal in 21 states and typically takes the form of "paddling," where the child is struck repeatedly on the buttocks with a long, wooden board.

In the 13 states where more than 1,000 students per year were punished, African American girls were twice as likely to be beaten as their white counterparts, the report, entitled A Violent Education: Corporal Punishment of Children in US Public Schools, said.

In the states of Texas and Mississippi, students ranging in age from 3 to 19 years were regularly penalised for infractions such as chewing gum, violating the dress code and fighting, ACLU and HRW said.

"Every public school needs effective methods of discipline, but beating kids teaches violence and it doesn't stop bad behaviour," said Alice Farmer, author of the report that looked at corporal punishment during the 2006-2007 school year.

Students with mental and physical disabilities are also not spared. In Texas, 18.4 per cent of those physically punished were special education students.

In 13 southern states where beating students is most prevalent, the report said African Americans were punished 1.4 times more than white students, even though their alleged transgressions were not disproportionately higher.

"Students that are dark-skinned, it takes more to let their skin be bruised. Even with all black students, there is an imbalance: Darker-skinned students get worse punishment," former Mississippi teacher Abrea T was quoted as saying.

Allison G, a recent graduate who was "paddled" as a teenager for being late to class, said: "I think there were several levels of emotion. Physical pain, mental humiliation. And being a female ... it was like there was this older man hitting me on the butt. That's weird - even at that age I knew it was inappropriate."

Educators who beat children have immunity under law and parents seeking justice for their children face resistance from police and the courts, HRW and ACLU said.

The two groups have demanded that the government prohibit corporal punishment in all public schools.

"I see corporal punishment as a form of slavery," the report quoted Doreen W, a school board member in Mississippi as saying.

"Think about the mental capacity that this kind of treatment leaves our children with. We are telling them we don't respect them." (dpa)