Some 128,000 fewer children attended industrial schools in Ireland between 1930 and 1970 than previously thought.
The Commission to Inquire into Child Abuse has radically reduced its estimate.
The commission investigated child abuse in industrial schools, reformatories and orphanages run by 18 religious congregations.
In a statement from its chairperson Mr Justice Sean Ryan on Monday, it corrected a report issued in May 2009 - which it says contained a "seriously erroneous statistic".
While it was initially believed 170,000 attended industrial schools between 1930 and 1970, it says this figure is actually closer to 42,000.
"In two places it states that the total number of children who were admitted to industrial schools between 1936 and 1970 was approximately 170,000", the statement says.
The commission says it has had correspondence disputing this total, citing the work of Professor Eoin O'Sullivan among others.
The chairperson consulted Prof O'Sullivan, Professor David Gwynn Morgan, the Department of Education and the other commissioners.
He is of the view that the number stated in the report is not correct, the commission says.
The commission says that previously, the total numbers of students in each school every year were added together.
But this did not take into account the fact many children would have attended for several years in a row.
The statistics provided by the Department of Education cover the period from 1930 and extend beyond 1970 - because some institutions continued to operate.
They also refer to reformatories as well as industrial schools.
The commission adds: "While it is not possible to establish a precise figure, the department's calculation of the number of children in industrial schools and reformatories from 1930-1970 and beyond is approximately 42,000 or somewhat higher."
Main image: The industrial school of Letterfrack in Connemara, Co Galway in the early 1900s | Image: Robert French/National Library of Ireland