When the intruders realised the classroom was occupied, they swore and ran off. But a few minutes later they were back. This time they threw an object at the two teachers before retreating. Unable to continue working, Ms Hughes and Ms Myatt left the classroom, but as they walked across the playground, the youths hurled abuse at them and then started throwing stones and other missiles. Although the teachers were not injured, they were badly shaken. “I felt very intimidated and powerless,” says Ms Hughes. “What came across was sheer hatred of teachers. It didn’t matter what sort of teachers we were or whether we’d taught them or not.”

Despite tighter security measures, incidents of this kind are on the increase, according to Sue Gormley, Ward End’s headteacher.

Ms Gormley has attended one of the Chase personal security training sessions and plans to use the company’s “Keep calm - keep safe” video with her staff later this term. But she doubts whether the advice would have helped defuse last week’s incident, which involved 14 or 15-year-olds.

“I think sometimes you can’t reason with lads of that age,” she says. “The video is very good in terms of helping you deal with an adult who comes in aggressively - and we’ve certainly had parents doing that.”