I certainly feel that they can refuse to acknowledge that bullying is going on. I was a very quiet child; shy and nervous, so as such I got left by myself a lot. Sometimes I think that if you come across as a loner child, teachers think you're bringing it on yourself. Told my parents what was going on after they noticed I didn't want to go to school anymore, and of course they go to the school enraged, accuse the Headmistress of condoning the bullying and an argument breaks out, but she at least said she'd do something about it. She didn't though.
The worst incident for me was when I sitting by a tree that was in the playground, and it had two foot wall around it. Some kid came over and asked if I wanted to play with him. Somehow or another we ended up on the wall, when suddenly a bunch of other kids came over led by his 'girlfriend' (how a 7 year old can have a relationship is beyond me). She was one of the worst ones for bullying me, and suddenly she shouted "Do it, now!" I feel two hands shove me in the back and I fall face first off the wall, hitting my nose when I landed. It sounds like something you'd see in a film, I know, but while I sat crying with my nose pouring blood, they ran around me laughing. The teacher in the playground eventually came over, and ushered all of those involved inside the school building, leaving me sat there clearly injured and upset by myself, and I remember feeling completely and utterly rejected. The look on my mother's face when she came to fetch me and saw the state I was in was something else...
I don't know what exactly happened when she went barging into the Headmistress' office, but it got results. I got roughly a months worth of peace and quiet and a letter of apology from the boy who pushed me. What bothers me though is why when my mum dragged me into the office, the other kids were sat nearby, but the Headmistress apparently had no idea what had happened, so obviously the teacher who brought them in said nothing.
The bullying carried on in high school, but by then I'd developed my coping mechanism of being sarcastic and using my vocabulary to confuse the shit out of them. I also started laughing at whatever they said to me; they really didn't like that. I got over bullying by myself, but as a result it's left me with a perpetually half-empty glass and I can be bitter sometimes.
Did the teachers know it was going on at both schools? Yes.
Did they do anything about it? No. No they did not; unless they were being threatened with being complained about that is. I understand there's only so much a teacher can do to stop it from happening, and I know that there are the odd ones who will go out of their way to stop it from happening. But in my experience, they were the least helpful aspect of the whole experience.
EDIT: Apologies for the long post. I didn't quite realise how much I'd rambled on.