Robertson High School was on lockdown for 15 minutes before the end of the school day.
It was the first lockdown at Robertson in at least two years, officials said.
Police said they received a report that two people were in a scuffle at a Robertson High School parking lot and that one broke the other's window.
Someone heard that noise and thought it was a gunshot, so that person called the school. Principal Eddie King then ordered all students into the building and put the campus on lockdown.
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