Staff and pupils from a Pinner school were kept behind after hours as police searched the site and investigated a sexual assault allegation.
Metropolitan Police officers came to the school, which getwestlondon will not name, with sniffer dogs and searched the premises on Wednesday (March 29).
A newsletter from the school to parents read: "We wish to confirm that there was never any allegation or search related to knives, drugs or other prohibited items.
"The allegation was one of sexual assault by one pupil against another. The investigation has been focused on establishing the facts around what occurred."
The Harrow borough school apologised for not answering parents queries and said staff were focusing on "keeping the school open and returning to normality as soon as possible".
A Metropolitan police spokesman told getwestlondon: "Officers attended the location. There has been no arrests at this stage.
"Enquiries continue to establish the full circumstances."
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