I think part of the problem is that it's a very difficult question to quantify - we can't control the inputs, we're not totally sure what we want from the outputs, it's unlikely that a uniform process will work to get the outputs we want, and we don't have the materials to guarantee a uniform process from start to finish.

On the input side, each incoming class is different: they vary across geographic and socioeconomic lines, they're all affected by factors which occurred years before we ever got them in a classroom to begin with.

On the output side, we really _Don't_ know what we want. It's easy to say, "students who can read, write, and do math," but the devil, as always, is in the details - how do we measure that in a way that doesn't immediately become a metrics problem á la No Child Left Behind?. More than anything, we need to foster successful individuals - but we're not sure how to do that on a large scale and the education system is but one part of a child's life.

The answer in a lot of ways seems to be "Very Good Teachers" - but what makes a good teacher? What sort of support structure is required? Are we willing to pay for enough Very Good Teachers? Do we have enough? Can we train more?

Further, to what degree does the attempt to constrain the education system so we can quantify the results inhibit individuality? In assuring a child knows his multiplication tables, are we imposing a system that will prevent that child from the free expression that would eventually lead to a great artist? Many of our finest works - the pieces of art by which we define our culture, spring from people who would, by any other metric, be considered failures by a system intended to raise successful individuals.

All this is complicated by the fact that the end result of a good education system ultimately is a good society - something we won't know until 20, 30, 40 years later. Everything else is a proxy: We think a high college attendance or graduation rate will get us there, we think more scientists and engineers will get us there, we think more well-rounded individuals will get us there, but ultimately, we don't know what makes a good society, nor what works to get us there.

I think there are improvements we can make, teaching methods that work better than others, and probably ways to quantify some of those differences, but ultimately, we don't even know the bounds of the problem we're trying to solve in education.