The teenager was assaulted by two other girls, aged 13 and 14 years, outside the Dobbie Hall in Main Street, Stenhousemuir around 3pm on Monday.
The young victim was taken to Forth Valley Royal Hospital with a serious but non-life threatening injury.
Sergeant Ally Goldie, of the Larbert community team, said: “This type of unprovoked sustained attack is totally unacceptable.
“This girl was targeted for no apparent reason and sustained injury as a result.
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“We are following a positive line of enquiry.”