PE teacher Darren Jones was in his office preparing for the day's lessons when he was shot with a pellet gun at close range. The incident happened at around 9.30am at Maesydderwen Comprehensive School in Ystradgynlais, Powys.
The schoolboy believed to be responsible was immediately taken into custody. Classmates described him to the Daily Mail as 'a loner' who was 'obsessed' with guns.
Mr Jones was heard shouting in agony after being hit in the chin by a pellet. Staff managed to grab the boy and the weapon was taken from his grasp.
Hugh Pattrick,, chairman of the school governors, said: 'It's very shocking. I feel very upset for the teacher and also for the boy himself.'
It is understood that police later raided the boy's home nearby, where they removed gun paraphernalia.
A neighbour told the Daily Mail: 'We've heard he was always boasting about shooting people in video games.'
In the hour after the incident, the school was shut down while police were called. A Powys council spokesman said: 'Staff dealt with the incident effectively and the school remains unaffected.'