At a secondary school where I worked as a teaching assistant, 'less' and 'fewer' used wrongly was a constant irritation, mainly in the maths department. Those maths teachers used to get fed up though, when other departments, especially geography and science, told the children they were using a bar chart rather than a histogram which was what they drew on the board for them to copy.
They could have sorted out this confusing (for the children at least) situation by talking to one another. Instead, my suggestion of 'fewer' instead of 'which children had 'less' pets' was laughed at in maths, and my point about calling it a histogram rather than a bar chart dismissed in geography.
SURELY the school departments should make sure that they are not 'breaking' grammatical or mathematical rules in their own subjects?
Ooooh and the science teacher who insisted on putting an apostrophe in the possessive its; it nearly drove me mad!