The 13-year-old girl attacked the Essex Valley School teacher at 11:04 a.m. on Wednesday, West Caldwell police said.
The two staff members sustained minor injuries while intervening, while the teacher initially assaulted was transported to Mountainside Hospital for treatment of undisclosed injuries, police said.
The Essex Valley School's website says it's a "comprehensive therapeutic alternative school that offers second chances to students who have not found success in traditional public and private schools."
The teen was placed under arrest and transported to the West Caldwell Police Department. She was charged with three counts of aggravated assault and was transported to the Essex County Juvenile Detention Facility in Newark.
Authorities did not release the nature of the teacher's injuries or provide further information.
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