Honestly, it's been hard for me to discern what you're trying to write about and what it is you'd like to discuss - SBG as an educational movement? The tension between SBG and grades? Calling on SBG advocates to defend their system so you can understand it/tear it down?That's mathymcmatherson pushing me to be clearer about my argument. In response, here's a brief summary of where I stand, without much in the way of justification.
- Your feedback system should not be your grading system. SBG is certainly a grading system, but many teachers think of SBG as also providing important feedback to their students. This is not a good idea.
- Your grading system should not be used to motivate kids. Grades -- and really all extrinsic rewards like badges, points, declarations of incompetence or mastery -- should not be used to motivate your students to learn math, because you want kids to have their own motivations to do good things, and cheap rewards are known to backfire. Yet many teachers use SBG to motivate learning.
- We know what good feedback looks like, and it's very good for learning. Good feedback helps learning by giving kids a chance to reflect and reengage with problem-solving, conversation, and all that good stuff. The Shell Center recommends questions as a particularly effective form of feedback. This is miles away from getting a "novice" on "Solving Linear Equations" or what have you.
- None of this is a reason not to use SBG. My real problem is with the way people think about feedback and incentives. I think that the way people talk about SBG reveals some problematic views on feedback and motivation, but none of this is an argument against using SBG. Use SBG if it helps, but your book-keeping isn't good feedback and you should expect any changes in motivation to come with some troubling side-effects.
I have other things that I believe, but these are the crucial bits.