I know this is a really old thread, but just thought I'd share my experiences, because it's interesting how different the ways the schools direct my students is.
I was told by my teacher numerous times, don't write expository essays, write creative, despite the fact that it wasn't my strength. They said that that's what the examiner wanted, so that's the way we should go for our (3 piece folio) SAC. In the end, I got in there and the topics didn't suit my creative drafts so I wrote two expository pieces and a persuasive hybrid.
The feedback was literally "I don't know why you didn't write an imaginative piece".
So yeah, sometimes schools push really hard for one style, but it doesn't mean all the schools are doing the same. I ended up not doing as well as I normally would, so maybe it would have been a better idea to ditch the expository and just do what my teacher wanted. I'm just not the sort of person who likes to be told that they should do something they're not as good at just for the sake of it (especially when the internal creative pieces we were told to write were anything but the 'out of the box' that they claimed they should be)