Brother Peter Carroll was called to give evidence at the Royal Commission into Institutional Responses to Child Sexual Abuse on Wednesday.

When cross-examined over how these "clusters" could have occurred at several Marist schools including Canberra's during royal commission proceedings , Brother Carroll said many cases were the work of one perpetrator.

But when was asked if poor governance led to the abuse clusters, he said that "can't be refuted".

"I think there were, you know, governance shortcomings. What they were ... was the centralisation of authority and the whole hierarchical model that was in use," he said.

"There could have been a very rigid control mechanism that was part of the culture of those schools."

The Royal Commission found Marist College Canberra had 63 claims of child sexual abuse made against the school.

This made the college the Catholic school with the highest number of claims in Australia.

But Bravehearts ambassador Damian De Marco believes the true number would be more than 100.

Brother Carroll acknowledged the harm and suffering the abuse perpetrated by Marist brothers caused in Canberra.

He said "structural problems" and a lack of oversight within the order could explain its poor response to claims of abuse.

"For instance, there was very poor administration, in one sense. It was very unprofessional. I mean, going back into the 1960s or before, the province administration was one man travelling around. There were very few supports. It was a very unprofessional sort of arrangement, in one sense, in terms of what we would regard as professional operation today," he said.

"There was also a very hierarchical model where everything had to be taken back to the leader, and the leader had to make the decisions. So I think that's another factor that led to the reasonably poor management of these things.

"Another could have been the whole lack of voice given to young people, so that the complaints were not brought forward by them, so that they weren't believed in some cases."

The Marist Brothers only began a study into child abuse in its own congregation last year, 20 years after the Christian Brothers commissioned a similar review.

Brother Carroll also admitted that was a "shortcoming".

"I think it's something that we should have done previously," he said.

"Initially it might have been some sort of sense of denial that the issue was as big as it has turned out to be, and then maybe that was a lingering issue. But other than that, I can't account for it, no."

The Royal Commission into Institutional Responses to Child Sexual Abuse will continue in Sydney on Thursday.