One in five secondary school children have been severely abused or neglected during childhood, the NSPCC said.
Almost a million children aged 11 to 17 in the UK were affected, with children being beaten up, hit with weapons, raped or seriously neglected, the NSPCC survey shows.
Andrew Flanagan, the charity's chief executive, said there are likely to be severely maltreated children in every secondary school across the country.
He said: "The scale and impact of child abuse requires a major shift towards earlier intervention in child protection. When children do not get the protection and support they need when they most need it, they can be vulnerable to continuing physical or mental harm and further abuse.
"There are likely to be severely maltreated children in every secondary school across the country. Some will face abuse and neglect while still at school. Others will have suffered abuse and neglect in early childhood."
The survey of more than 2,200 children shows 18.6% had been physically attacked by an adult, sexually abused, or severely neglected.
Only physical abuse which resulted in an injury, such as bruising or a broken bone, or which involved the use of a weapon was included in the survey, the NSPCC said. Smacking was excluded.
Sexual abuse was only counted if it involved a physical element and efforts were taken to exclude instances of consensual sex among young people. Severe neglect was restricted to a constant pattern of neglect, such as children going without food or clothes, or never being praised or told that they were loved, the NSPCC said.
Children's minister Tim Loughton said the report's findings are "particularly poignant and demonstrate the impact public awareness and action has had in cutting levels of abuse".
He also announced that an £11.2 million grant will be given to the NSPCC over the next four years to "help them to deliver an important frontline national service for the most vulnerable children and young people in our society".