Re "No Child Left Behind"

It seems to me that there is a very easy way to obviate some of the problems with No Child Left Behind - which is to simply redefine the notion of "grade level" itself. Why shouldn't we determine "grade level" (which is an arbitrary and artificial construct anyway) not in terms of chronological age but in terms of a student's actual level of achievement?

Clearly a student could be at different "grade levels" from subject to subject - but if curricula were constructed in such a way that a student could move through them at relatively independent paces, achieving "certifications" as they master given bodies of knowledge, I don't see that as being a problem. It is exactly what we do within certain realms of the corporate world, such as IT or HR. We need to decouple the notion of academic progress from its present lockstep relationship to chronological age.

If we can do this, I believe we can strip the people who are presently trying to cripple public education by means of NCLB of their most potent tool, while still allowing educators to be evaluated in terms of effectiveness and establishing realistic standards for student progress.