Could This Explain Administration's Love of the Differentiated Instruction Fad?

From a comment at Joanne's blog:

There are a few exceptional teachers who can “differentiate” over a wide range of abilities and preparation and motivation. But most can’t. However, wishing and hoping that ordinary teachers can do it allows everyone to avoid facing some very, very, very unpleasant truths.

Though people disagree on the reasons, everyone knows that separating children on the basis of how quickly they are learning will result in faster groups with an “over-representation” of whites and Asians, and slower groups with an “over-representation” of blacks and hispanics. No one wants that, and a simple way to keep it from happening is to put everyone together regardless of preparation, aptitude, and motivation.

It's also cheaper to lump kids together and say "teach them all".