It followed soon after an apparent  industrial relations dispute at De La Salle college in Andersonstown.
It is understood on Wednesday, more than 25 teachers out of a teaching staff of about 70 called in sick.
It is believed a dispute at the school, which has about 1,000 pupils, centres on an incident prior to half-term.
Many of the teachers are said to be concerned over the way it was handled and sent a letter to the principal.
At one point, for a brief time, a large number of teachers stood silently at the doors of classrooms.
A staff meeting on Monday, when no pupils were in the school, has been described as robust.
So far, there has been little comment from teaching unions.
INTO, which represents most teachers in the school, said that it and other unions are attempting to resolve what it described as an "industrial relations issue".
It is understood that about 15 teachers called in sick on Friday.
The Council for Catholic Maintained Schools has said there will be meetings next week involving it and the Board of Governors and unions.
About a third of the teaching staff at one of west Belfast's biggest secondary schools called in sick one day this week, the BBC understands.