In a statement on Cwmcarn High School's website, headteacher Jacqui Peplinski said "concerns were dealt with swiftly".
"There was no risk to any staff or learner and the relevant support services were contacted as a precautionary measure."
"Cwmcarn High is a caring and safe environment and we are committed to everyone’s safety."
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Showers in the north will spread southeastwards overnight. Temperatures will be higher so not as chilly as list night.
Chilly start to Tuesday, turning into a largely fine and dry day.
Political Editor Adrian Masters was joined in the studio by assembly members Bethan Jenkins, Mick Antoniw and Suzy Davies.