One GD was bullied by a particular girl from the moment she arrived in school. Recently she said to me 'I don't want to become 10 years old, because it means '*' has been bullying me for half my life'. For a few years she was able to cope with it, but it is relentless, and has worn her down to the extent that she spends Sunday nights crying that she doesn't want to go to school. DD has tried talking to the teacher each year, talking to the head teacher, but the school only asks the other child if they have done what ever it is, and when they say 'no' it goes no further. DGD has kept a diary and shown it to the school, but only gets the same reaction.
Nothing brutal, just treading on her heels, sticking an elbow in her ribs, pulling her hair, calling DGD a 'brat' and a cry baby. She has two more years of this before secondary school, when they will be going their separate ways. One girl has actually had to move schools because of the bully, you would have hoped the school would have done better.
But for that reason, I would advise a very early approach to the school to nip it in the bud.