Authorities told local media that the 17-year-old injured on Saturday had been taken to hospital, but her condition is not life-threatening.
Schools in Poland had been stepping up security following knife attacks at schools across the country on 7 and 8 October.
On Wednesday, a 19-year-old student attacked and injured nine people at a vocational school in the central Polish province of Mazovian.
Polish police had already deployed to schools after a female caretaker was killed and several others injured in two earlier attacks in two days.