My colleague next door has laid out a bit of a standards-based grading manifesto.  Read it here.  You'll be hooting and hollering or extremely furious, depending on where you stand.  Either way, it will get you thinking.  A few snippets to wet your reading appetite:

On the problem with traditional grading schemes...

Prob­lem: Kids want to play games to get points in order to get an ‘A’. This is a prob­lem because it puts empha­sis on accu­mu­lat­ing points and not on what the points are sup­posed rep­re­sent: learn­ing. You must migrate your sys­tem of grad­ing away from grad­ing every sin­gle assign­ment sum­ma­tively (that is assign­ing a sta­tic grade for every­thing a kid does), and towards grades that are indexed by content.
Stu­dents could not care less about their score on “Quiz 5″ from last month; they don’t even know what was on that quiz. Don’t put that in your grade­book. Put the indi­vid­ual ideas that that quiz assessed in your grade­book, so that the stu­dents know what it is you care about. I do this, and my grade­book has bal­looned to about three times its pre­vi­ous size. Oh well.
 and some thoughts on implementing standards-based grading so students understand it...

Major Hur­dle: Kids don’t lis­ten on the day you present the syllabus/explain expec­ta­tions, so they won’t under­stand your new grad­ing sys­tem. You can bela­bor the point for the entire first day (why are you spend­ing a whole day on the syl­labus? Get going; they can read), but the stu­dents are so dead to class­room logis­tics that you’re going to have to teach about SBG as they go along.
I have many moments through­out the semes­ter where kids show me how trained they are by the pre­vi­ous sys­tem. Kids will ask me if they can do extra home­work to raise their grade. Why the hockey sticks would some­one ask that? It’s absurd. I don’t even grade home­work!! I say, “No, but you can study and show me that you under­stand this topic from a pre­vi­ous chap­ter that you’ve pre­vi­ously demon­strated a low under­stand­ing of.” They usu­ally snap back into our real­ity. This is the behav­ior I’ve wanted all along, and I’m happy to say I have it now.
Tweet about it.  Send it to your colleagues.  Post it to your listserv.  It just makes sense.