I was a student at Alverno in the 1970s when the ability-based curriculum was relatively young - and debated. That the eight abilities have remained stable (though adapted I'm sure) and the model fairly well aligned with its launch says a lot about the success at least one institution has had with it.

As a student, I would gladly have traded abilities for grades many times. The process was rigorous. Jade mentioned the outside assessors, but self-assessment was also built in. Parsing HOW an essay or a report or a speech for that matter was good (or bad) rather than just sitting back and receiving a teacher's judgment on it helped to integrate the lessons of every variety. That habit becomes ingrained (in my experience) and is hard to shake.

I'm not an instructional designer or teacher (my husband, who is, passed this mention on), but I have appreciated the value of the learning environment I experienced many, many times in my career as a writer, editor and consultant.