Police were called to St George’s school in Gravesend on Monday to reports of a disturbance.
A boy was arrested in connection with the incident at the Meadow Road school and later released without charge.
Head Anne Southgate described it as “unacceptable behaviour” which was dealt with quickly.
Rumours that a pupil had threatened a member of staff with a pair of scissors were dismissed.
She said: “This isolated incident was dealt with swiftly using the school’s behaviour management systems.”
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