Search the archives for what Chris Olsen has said about this. I certainly cannot speak for Chris but at least twice on this newsgroup I think he has said that any scale (transformation, alteration of numbers written at the top of student tests, what ever you want to call it) that does not take into account spread (standard deviation) is "witchcraft" (Chris, I hope I quoted you correctly). Unfortunately most school administrators either don't understand this or don't wish to face parental inquiries into what a standard score means.
I too am faced with a school mandated, publicly posted scale of 90-100 A, 80-89 B, etc., from which we are not supposed to stray. I would love to be able to use some sort of standardized, composite scores. Alas there is no chance of that ever happening.