According to ANN News, the 14 year-old allegedly grabbed a pen off the teacher's desk and then stabbed her over ten times in both shoulders. The teacher later filed a report, and the 14 year-old was arrested and apologized for the incident and said, "I got ticked off by her warning me."
Thankfully, the injuries were not serious, and the teacher recovered from them in a week.
注意され…男子生徒が女性教師をペンで10回刺す [ANN News]
授業中にボールペンで女性教諭刺す 漫画本注意され容疑の中学生逮捕 [産経ニュース]