To put everything back within the analogy
klash describes--which was
quite vivid, actually--I see what
klash is saying, but
Orange Julius
is correct when he says that public schools generally don't try to make
all kids the same brick.
To sprinkle some math on, I think it'd be more correct to say that
schools are able to deal competently with bricks that are within one standard
deviation in either direction of being average bricks--you just add
varying amounts of cement, and you can still make them all fit in the wall
nicely.
The problems arise when you get bricks that are way too small or way
too big. The really small (dumb) bricks aren't worth putting into
the wall, and conventional bricklaying logic says to discard them.
Schools are not bricklayers in reality, however, and must deal with the
social and ethical consequences of throwing away the small bricks.
Since they can't ethically throw away any bricks, they have
to put all the really small bricks in a corner, throw the third-rate cement
on them, and try to slap a special wall together.
And the really big (smart) bricks, those require too much cement to
get them to fit into the wall. It also requires restructuring all
the other bricks around it to make a nice fit, which slows down the bricklaying.
Since schools can't throw them away, they generally try to either
A) Pretend that the big bricks aren't all that big and hope no one notices,
or
B) Let the big bricks go to a more advanced stage of bricklaying before
they're emotionally ready (Okay, so the analogy is a little weak here.
Sue me.) to get rid of them.
So, while the shotgun system makes really good, stable, medium-sized
brick walls, there's a pile of leftovers that all the politicians are conveniently
ignoring.