School staff said they were “incorrectly advised” that a woodwork area could be used after asbestos dust temporarily closed other classrooms.
Pupils were allowed into the room at Nairn Academy before it was shut following concerns about dust.
Tests confirmed that the dust found last week was white asbestos.
In a letter to parents, the school said it had been advised by NHS Highland and Highland Council that the risk to health had been “low”.
Asbestos dust was discovered in some parts of the school in Nairn last week following work over the Easter break to remove moss from the building’s roof.
The affected areas of the school were closed from Monday to Thursday last week so they could be cleaned.
The woodwork area was removed from use on Wednesday after earlier advice the area was not affected.
The woodwork area has also been cleaned.