Schools Without Grade LEVELS!

A Colorado school district is implementing major reforms, including doing away with grade levels. Instead, students will work on key skills until they demonstrate mastery (at a 'B' level), then they will progress to new material at their own pace (which may be different in different subjects).

You can see more details in an online article, but there are some interesting aspects to this approach. I'm very curious what it will do to the notion of social promotion. Will there be students who remain stuck multiplying fractions and decimals on a 6th-grade level for 6 years? Because we've got that now.