If you are having a problem, my advice would be to get something to the school in writing, pointing out that you now consider them to be on notice of the problem and their actions (or lack thereof) will be noted and acted upon, if needed. Also ask for a copy of their anti-bullying policies in writing and what efforts they undertake to ensure the student body and staff comply.
In legal terms, this is 'setting the stage'. You are putting them on notice that you are watching and that their actions will have consequences. Any decent school administrator, or their counsel, will recognize this and ensure some actions are undertaken.
Best to document any instances as well. The more detailed you are (dates, incidents, names of children, staff who were on duty, etc) the more nervous you will make them. If you have emails of the any GSIS parenting groups you can bring them into the discussion as well.
In the meanwhile you might also look at some of the anti-bullying resources around the net to give your child some added instruction on how to deal with things.