It began with one of the children asking: “Is she always like that? She shouts at you like she does at us.”

I must have looked puzzled because, before I could say anything, he added:

“I don’t mean you on your own, but all of the teachers. She shouts at everyone.”

The fact was, we had all become inured to the behaviour of one of our colleagues. This lady, let’s call her Mary, was a head of department and senior teacher, and the boy was quite right - she did shout at children, staff, and even parents at times.

Mary had always been a “character” who made sure that her views were put forward in school, but lately things had become worse. Much worse.

It was almost as if we had developed collective deafness, and Mary’s response was to yell rather than talk, even on a one-to-one basis.

This particular day was a Friday and, as usual, we had gathered at lunchtime to read the late Ted Wragg’s column and were enjoying it when Mary came into the room.

When she saw us huddled round the paper, Mary immediately launched into a full-blooded assault on us. But instead of backing off, it was as if we had one collective thought and the four of us totally ignored her. It was only afterwards that I heard she had gone to the toilets and wept.

I was staggered. I had no idea that her need was such that we should have stopped everything and paid attention to her. She had not known what we were doing when she walked into the room, but had immediately assumed that, because there was laughter, it was at her expense, even though the paper was on full view.

It was only when someone pointed out to her that it is not unreasonable for teachers to read The TES at lunchtime that she realised her misjudgment and apologised.

It is difficult to pinpoint the tipping point that affected Mary, but it was certainly something that crept up on us. It was behaviour that had worsened over time, but which no one had latched on to. Mary’s aggressive behaviour was masking something deeper.

In fact she was a scared, insecure person who coped by being aggressive and downright rude to everyone. It is only with the benefit of hindsight that it is possible to see the warning signs. Mary was heading for a nervous breakdown.

Her personal relationships with other teachers were deteriorating, yet no one saw the signs. She found classes that were previously challenging impossible to deal with and her administration was simply falling behind.

Children with whom she had previously had a good relationship were disrupting lessons, and her marking had fallen weeks behind.

Everyone knew it, but in the hustle and bustle of daily school life everyone missed the vital signs. It took a child to ask: “Is she always like that?”