Just been to parents evening and as we were waiting we could look through our DC's work. We saw IRS written a lot over all of the DC's work, all the parents sitting there were equally baffled, we were asking each other but none of us knew what it could be! DH reckons it's the US taxman but I'm not sure that DS's maths is good enough for him to have been headhunted by them yet 
Can anyone help please? It's the sort of thing that will drive me potty if I can't find out the answer...