An audit of how the Catholic order the Christian Brothers dealt with abuse allegations has found only 12 brothers were convicted of crimes between 1975 and today.
A review of the congregation's files found that its initial response to the need to report abuse to the authorities was not systematic and was inadequate.
It revealed allegations were made against 325 brothers - only 50 of whom are still alive - with 870 complaints of abuse in the 38 year period, all of which have been reported to authorities.
The latest and largest tranche of reviews by the oversight body, the National Board for Safeguarding Children in the Catholic Church, scrutinised both current practice in two religious orders and six dioceses and the handling of all allegations received since January 1975.
In the Christian Brothers, the inspection board said one brother was returned to ministry after an allegation and only 12 brothers were convicted of offences against children.
It described the level of abuse from members of the order as substantial.
And it warned: "The number of convictions by the courts, compared to the numbers accused of child abuse, is significantly small."
In the 66 years between 1931 and 1997, the Christian Brothers received 92 allegations of abuse but in the subsequent 15 years, from 1998 to this year, they received 794 allegations.
Since internal reviews in 2007 and 2009, the safeguarding board said it is now satisfied that reports are made promptly.
The Christian Brothers said they accepted that a safeguarding deficit existed in the past.
"We want to learn from the mistakes of the past and to create a safe environment for all children and young adults," it said.
The Kiltegan Fathers, also known as the St Patrick's Missionary Society, were also inspected and criticised for in adequate recording of allegations, incidents and suspicions.
According to the watchdog, a total of 50 allegations were made about members of the order in the 38 year period.
The allegations involved 14 individuals - nine of whom were still alive when the review was taking place - while five have left the order.
One member of the order has been convicted of an offence against a child or young person over the last four decades.
The watchdog said "too much tolerance" was given to priests accused of abuse and also cited instances of children who claimed to have been abused by missionaries.
The watchdog said abuse outside the Irish region was not always met with appropriate and robust action and that children outside of Ireland were not given the same level of priority.
"Accused priests were afforded too much tolerance and so found it too easy to avoid being held accountable for their actions," the report said.
"It also appeared to the reviewers that the identification of abuse of a child on the missions did not always evoke the actions that evidence an empathic response to the experiences of victims."
Kiltegan society leader Father Seamus O'Neill apologised unreservedly to victims of abuse and their families.
"We remain committed to attaining best practice in safeguarding children as soon as possible," he said.
Elsewhere, the watchdog found the organisation had completely failed to meet requirements of having a written plan in place on what steps should be taken to keep children safe.
A series of reports on dioceses around Ireland, north and south, were also released.
For more, visit: http://www.safeguarding.ie/