Just a happy anecdote for all you worried parents....
My DD was bullied by one girl in year 2. It was the typical girl stuff- telling others not to talk to DD, hiding her things, nasty comments. DD didn't seem to care as she had her own friends and had written this girl off as 'just not very nice'(DD is not a fragile child and tends to let things roll off her back). DD's friends were upset on DD's behalf and told the teachers who phoned me and the bully's mum. It turned out that the bully was having a hard time at home and while the low level meanness didn't stop completely, it didn't escalate and they were put in different forms for the rest of primary school. The bully still fixed on DD as her hate object but never managed to get a reaction out of DD.
Fast forward 6 years....
Bully is now one of DD's best friends. A bit of growing up works wonders.