The giant fake animal was taken some time during Monday night and was reported missing this morning when staff noticed the equestrian statue was missing.
It had been secured to the ground with metal bolts and Alison Marsh, PA to the headteacher, said: "I don't know how they managed to take it and get over the fence, it's enormous and very heavy."
The horse was painted by pupils at the school earlier in the year as part of a World Cup themed event at The Racecourse Newbury.
Police have confirmed they are investigating the incident and anyone with information should call 101.
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