A female teacher suffered a broken jaw and a male teacher was attacked with a 950,000-volt stun gun, in an assault outside a Bristol school.
One teacher remains in hospital
The woman was punched in the face when she went to help the male teacher as he was attacked with the stun gun and punched to the ground.
The attack took place outside Ashton Park school, Bower Ashton, as the teachers left during the lunch break.
Police believe the male teacher was targeted by a youth.
The attacker and another man left the scene in a black Vauxhall Corsa and police are appealing for witnesses.
Police have recovered the gun and are making inquiries about the attack on Thursday.
Detectives believe the attacker may have been waiting for the male teacher as he left the school.
Acting Det Ins Guy Worrall said: "The male teacher was attacked first, then the female teacher came to his rescue.
"She was punched once to the face, suffering a broken jaw.
"The attacker possibly had some connection with either a former pupil or current pupil.
"He called the teacher's name then ran down the road after him before using a stun gun on his back.
"The male teacher felt a sharp pain to the back and was then punched several times before falling over a wall into a garden."
The stun gun was recovered at the scene
The attacker, who is described as being 16-20, of mixed race and 5ft 10ins, was part of a group of youths who were waiting outside the school gates.
The male teacher has returned to work, but was said to be "very shaken" by the incident.
His colleague remains in hospital having treatment for her injury.
The stun gun used in the attack is known as a Viper Defender and is sold in South Africa.
It is a "terrifying deterrent" according to the maker's website.
The device is said to deliver 950,000 volts, "causing extreme pain, muscle spasm, disorientation and loss of balance".
Police said the gun was classified as a firearm and was banned in the UK.