The action was taken by St Columba's School in Inverclyde after details of police investigations came to light.
Police Scotland confirmed that it was investigating a recent allegation involving a young child.
A 56-year-old man has also been reported to prosecutors over alleged historical abuse of a 15-year-old girl.
A Police Scotland spokeswoman said: "We can confirm that a complaint has been received regarding a sexual assault on a young girl.
"Enquires are ongoing to establish the full circumstances and it would be inappropriate to comment further at this time."
On the other allegation she said: "A 56-year-old man has been reported to the Procurator Fiscal in connection with non-recent alleged sexual abuse of a 15-year-old girl."
The co-educational school, based in Kilmacolm, caters for about 700 pupils, with annual fees of about Â£11,000.
Two teachers at one of Scotland's leading private schools have been suspended amid separate allegations of sexual abuse of young girls.