Former headmaster of Knox Grammar Ian Paterson deliberately covered up allegations about child sexual abuse because he placed the reputation of the school ahead of student welfare, a royal commission has found.

The Royal Commission into Institutional Responses to Child Sexual Abuse has delivered a scathing assessment of Dr Paterson in its report into how Knox Grammar and the Uniting Church handled multiple allegations about teachers over a 40-year period.

Dr Paterson "deliberately withheld information" from a police officer who was investigating sex abuse allegations at the school, the report found.

He also failed to notify parents of the boys who had made allegations and did not inform Knox Grammar's school council of sex abuse claims.