The pupil, previously excluded, had wielded an air pistol that could seriously injure at close range. He later apologised and no further action was taken.
She told The TES she is now thinking of leaving the profession because of several incidents of threats and violence which had led her to take time off with stress.
Her trauma is not unusual. In a survey of 433 teachers by the Teacher Support Network, published today, nearly all had been verbally abused and half of them physically abused. Four said they had been assaulted with knives, three with guns. Others had been stabbed, strangled or, in one case, attacked with a fire extinguisher.
By comparison, in a smaller 2005 study, only one in five had been physically abused, and none had faced knives or guns.
In the past two school years, authorities in Birmingham, Barnet in north London, and Merthyr Tydfil in Wales all excluded more than 50 pupils for carrying weapons, according to data released under the Freedom of Information Act. It showed weapons included airguns, scores of knives and a length of pipe. One 13-year-old from north London, Hakeem Johnson, was excluded from Homerton college of technology for threatening a teacher with a hammer. Later, he shot dead the owner of a fast-food shop. He was jailed for life last year.
Patrick Nash, Teacher Support Network chief executive, said violence and abuse could devastate teachers. More than a third of respondents had been forced out of work to recover from injuries. Most said if their school had a code for bad pupil behaviour, it was not properly enforced. Mr Nash said the network offered help but more was needed.
Teachers who had suffered pupils' violence did not want to be identified, so names have been changed. One said a pupil had hurled a projectile at her, cutting her eye. She sought the head's help but was told to complete her lessons as no cover was available.
The findings come after a spate of shootings in south London, culminating in the death of 15-year-old Billy Cox last week, which have fuelled concerns over youth violence. Youth workers say guns are available from just pound;50 on the streets and can be bought from minicab firms and sweet shops.
Uanu Seshmi, director of the From Boyhood to Manhood Foundation, said boys as young as 11 are being led into the criminal world by older brothers, and children aged five are familiar with gang culture.
One south London head said about half the pupils he had excluded were in gangs, with six pupils in each year mixed up in weapons and stolen goods.
He said police were "useless" and failed to warn schools of repeat offenders in their midst.
Gang victim Billy Cox is thought to have been excluded shortly before his death.
Steve Sinnott, general secretary of the National Union of Teachers, said:
"I don't think we should blame schools. Heads don't like excluding pupils but sometimes have to for their own protection."
This week, the parents of the murdered lawyer Tom ap Rhys Pryce said they had raised pound;815,000 to help prevent deprived children turning to violent crime.
Kenny Frederick, head of George Green's school in east London, says in today's TES that schools should talk to pupils and parents about ways to make their communities safe (see page 27).
Teacher Support Network helpline: 08000 562561