Great question, Carol. Why do we need to ascribe grades? What do grades even MEAN (that’s why the ending of my post was playing around with the meaning of an “F”, “B” and “A”, because these things are truly arbitrary – giving them numbers or making them built on numbers also means very little).
There was a great twitter chat via #digped recently about that question – the Storify is available here, if you’re interested: http://www.hybridpedagogy.com/page-two/digped-storify-assessing-assessment/