Two leading Roman Catholic schools "prioritised monks and their own reputations over the protection of children", a report says.
"Appalling" abuse was inflicted on pupils at Ampleforth in North Yorkshire and Downside in Somerset over 40 years, the Independent Inquiry into Child Sexual Abuse (IICSA) said.
But, the report said, both institutions attempted to cover up the allegations.
Ten individuals, including monks, have been convicted or cautioned for abuse.
The report, based on evidence heard by the IICSA's investigation of the Roman Catholic Church and the English Benedictine Congregation, said, however, the true extent of the abuse is "likely to be considerably higher" than the number of convictions.
It states many of the perpetrators did not hide their sexual interests from the children and pupils were often abused in front of each other.