My personal stereotype of the playground bully is like an Identikit picture pieced together from school thugs I once knew and loathed. Hefty girls with their cardigans slung across their shoulders, boys with cropped hair and shirts hanging out - you could spot them a mile off.

Not at all like my sweet six-year-old who skips off to school with her hair in perfect plaits. Not my tender-hearted girl who weeps when others hurt themselves and clings to friends like a limpet to the rock. I could believe she'd be the victim, but not a victimiser.

The distraught mother at my front door had a different story to tell. Angela is a familiar face in the parental crowd at our local primary school. Her son Adam, nearly eight, and my daughter, Polly, are in the same class. 'It's all rather embarrassing . . .' she said. 'May I come in?'

Apparently Polly had been disrupting Adam's games in the playground. With a mixture of discomfort and relief, Adam reeled off the charges against my daughter. I could feel the smile slowly draining from my face.

It seemed Polly had been systematically hounding Adam, hitting him, calling him names and spitting at him. He (not surprisingly) had been utterly miserable and fearful at bedtimes. Angela had put off coming to tell me, but after several weeks the situation did not seem to be improving.

Part of me wanted to fight back with the parent's pathetic volley: 'No, not my child.' I always fondly imagine my children to be on their best behaviour when out of my sight. Polly, to my knowledge, had not hit another child since she was a toddler. Then I saw a mental picture of my child spitting at another, and I was furious.

Angela left in more embarrassment than she arrived, tripping over apologies on her way out. In fact, I was unsure how to proceed. I had no blueprint to follow and suddenly found myself overwhelmed by a sense of dislocated shame. It felt as though I was the one who had bullied her poor child.

I marched down to the school, just as parents are supposed to do in these situations. I sensed all eyes on me. Would you stop and chat so pleasantly, Mrs Jones, if you knew what my daughter had done? And yet this was my daughter and I wanted to be forgiving, and understanding, loyal. This felt like a family affair - we were all in it now.

I was not looking for a scene, rather to limit the damage. Adam would not have to spend one more playtime in tears. But confronted quietly in a corner of the playground, Polly pleaded innocence. As I looked down into her trusting eyes, I thought 'Oh my God, what if I'm wrong. What if Adam made it all up?' She was so plausible in her bewildered defence. And then, without warning, she burst out crying: 'How did you know?' she sobbed. 'Who told you?'

With her tears came my instant forgiveness, the forgiveness of the doting mother which, perhaps, only other doting parents will understand. But we had a lot to talk about.

Curled up in the duvet that weekend, Polly and I had the heart-to-heart she had been avoiding for a long time. Beneath her sunny exterior was a turmoil of emotion. If she had bullied Adam it was not to dominate or hurt him - it was out of love.

At school, a range of catching-kissing rituals had risen like the sap in spring. In one game, a girl is banished to a corner of the playground while her friends guess her boyfriend. The girl returns to be confronted with the name of her true love and confess to the accuracy of their whisperings.

It soon became obvious that Polly's real love was Adam, who had sent Polly a handmade Christmas card - his mother had told me it was the only one to 'a girl'. And Polly, more recently, had declared apropos of nothing: 'I hate Adam Green.' As she said it, she had blushed as violently as the young Princess Di.

Polly's version of events in the playground did not square perfectly with that of her accusers. The spitting was an over-reaction to being 'caught' by Adam in a game. He had spat back. The hitting was 'getting too near with my skipping rope'. And she still insists she did not call him names.

But the details are less important than the whole picture. Polly had been trying to goad Adam into a kind of reaction, to pay her attention. Now she understood she was hurting him, and that he was as frightened of her approaches as she was scared by the power of her own feelings.

She desperately wanted to make amends and wrote him a note in her best handwriting and spelling:

'Deer Ad, I am sorry if I hert you. I did not meen to upset you. I hop we can still be frends. Love from Polly XXX.'

Underneath was a picture of the two of them holding hands and flying kites in a park with smiling flowers. We delivered the letter and Angela reported that Adam thought Polly 'awfully brave' for writing it. Polly, as far as I know, has since left Adam alone. The sad thing is that they don't seem to play together at all any more. But I caught the two of tham smiling coyly at each other over a desk at the last parent- teacher evening. Who knows, this could still be the start of a beautiful relationship.