Children witnessed a supply teacher being stabbed in the stomach with a kitchen knife as he began to teach a science lesson yesterday morning.
The attack on Vincent Uzomah (50) at Dixons Kings Academy in Bradford sparked a police hunt for a 14-year-old boy who fled the school after scaling a fence.
The teenager, a pupil at the academy, was arrested in the city centre about six hours later on suspicion of attempting to murder the teacher, who had only worked at the school for a few weeks.
Mr Uzomah was taken to hospital with a wound to his stomach but is said to be stable and his condition is not thought to be life-threatening. It is understood he was stabbed with a kitchen knife.
Parents who gathered outside the school after hearing the news said the school had a good reputation for discipline but were concerned about the effects on their children.
The school is 15 miles from the Corpus Christi Catholic College, in Leeds, where teacher Ann Maguire was stabbed to death by a student just over a year ago.