Hi squishy, just read your thread 'Darwin Delusion' and wanted to add my support to you and agree that writing to the school is an important step.
This has come up locally for us as there is a public meeting on this subject near the school my daughters will go to. The person giving the talk locally to us is a headteacher of a 'good' school!
We are getting all the people we know with any sound knowledge of evolution and ability in public speaking to go along to the meetings. (I think it helps if some are also Christians - we know a paleantologist who is a Christian who is interested in helping.)
It was also becoming an issue where we have moved from and as a Christian myself I am aware of a number of organisations which modern churches are affiliated to which seem to support anti-evolution teaching. Some people were not allowing their children to attend science classes where evolution was being taught, which is very sad. The next step seems to be to insist that their ideas/ beliefs are taught and available in schools as an alternative. Schools have to listen to parents, so it is really important to get people to write and take into account the reputation of the school and the the effect it will have on other students. Bear in mind that the people running the talks will have some parents writing in too.
I know it can seem a lonely road sometimes to stand against this sort of thing, but rest assured you are not alone. If there's anything I can help with, get in touch.

Stay cool. Let us know what happens. :)