DemocracyNow! featured a very interesting segment today, about the latest salvo of the business-model of education, in which the governments of Chicago and New York publicize rankings of teachers based on how the kids do on standardized tests. (The theory is that these tests will tell us how much value each teacher adds.)

It’s a good segment which demands a fundamental question: How much value should teachers be expected to add? And how can we measure this value?

Fortunately, the BBC recently broadcast a program in its Analysis series called Do Schools Make a Difference? The short answer, of course, is yes. But the key follow-up is: How much of a difference do they make? Let’s go to the transcript.

Here’s something to think about. There’s a lot of academic debate about what makes a good school, but there is consensus on one issue. Time after time, serious, well-sourced studies tell us the difference schools make is very small indeed. Professor Harvey Goldstein can help — with a statistic:

GOLDSTEIN: After you’ve adjusted for the achievements of children when they start school, there are further effects related to their social background and to whether they’re a boy or a girl, to their ethnic background. These background factors — social class, income and all the others — have very important effects very early on in childhood, and of course these persist throughout schooling.

ABRAMS: Just to be clear really. I mean how … You’ve compared all those background effects to the school effect. How important is the school effect?

GOLDSTEIN: The school effect tends to be rather small. Once you’ve taken account of all those, maybe it accounts for 10% of what’s left, which is not enormous.

ABRAMS: Let’s just go over that again. About 10% of a child’s life chances are actually down to his or her schooling. The other 90% is down to parents, family background, social class. Stuff that’s already fixed well before your child ever goes through the school gates, clutching his Bob the Builder lunch box.

I wish to be clear, and anyone who knows me knows how seriously I take the point I am about to make: I am committed, with every fiber of my being, to getting the most education and intellectual opportunity out of that 10% effect that I possibly can.

(And, as the program makes clear — it’s a very good program, you should listen to it — teachers like me are caught in a trap. We must go into school every day, knowing that we’ll probably have little or no effect on our students’ lives, but determined to make it happen anyway.)

Without trying to boast, I believe I have changed students’ lives for the better. I believe that a great teacher can help a struggling young person turn her/his life around. And I believe we teachers must be adamant about constantly improving ourselves, so that we don’t waste a single moment of opportunity when that 10% window opens.

However, at the same time, it makes me sick to see government officials — and business leaders, often working hand in hand — creating ludicrous expectations for teachers, expectations which presume a 40% or 70% or 100% level of influence. And then firing teachers and closing schools when these expectations aren’t met.

A cynical observer might suspect that these systems of expectation are destined to fail, and that this whole wave of business-model reforms is nothing but a wholesale attack on the existence of public education itself. I’m not that cynical, and I always try to assume good faith.

But there is no question that these attempts to “reform” schools are foolish and dangerous, and in the long term they result in less quality education for those struggling students who they are supposedly being enacted to help.