Were any of you in band? There was a "first chair" idea. Essentially, the best people were ranked highest. Skill was determined anonymously. At any time, you were able to improve or lose rank.
Why can't we simply do something like this in all subjects? The best brains are all grouped together and given the most attention. If anyone in that group can't keep up, they drop down to the next group down. If anyone in the lower group wants to improve, and is able to, they're welcome to.
Why can't we implement something like this, if we really want to be competitive in the world. Yes, it would hurt the feelings of the kids that weren't in the top group, but only if we keep telling everyone (starting at birth) that you can be anything you want to be. (I want to be a world-class sprinter, but I don't think that's going to happen no matter how much I work on it.)
The pace being slow isn't necessarily the fault of the teacher, it's the fault of our expecting the best minds to be grouped with the middle minds.