Ebbsfleet Academy has banned parents from entering without an appointment after staff were subjected to verbal abuse.
The ban was put in place after a minority of parents had been "violent and abusive".
One mother's outburst, where she was shouting and swearing, was recorded in the school's reception area.
Principal Alison Colwell said some parents had been banned for the safety and wellbeing of students.
Some of the behaviour was the worst she had seen in her 25-year career, she said. "The students don't deserve to witness that, to hear that. My staff don't deserve to be subject to that. All of the people that work here are totally committed.
"As part of your working life to have to take that level of abuse is just unacceptable."
Julie Huckstep, from the Association of Teachers and Lecturers, said: "It's the first instance that I've heard of, certainly in this area, of violence from parents towards staff.
"But yes, teachers need to be protected. If you go to any public building, there are signs saying 'we won't tolerate violence' and why should schools be any different?"
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