There is a problem, and that problem is her and me, and all the other parents who will never be satisfied with just a good enough education for their children, but who want the best they can lay their hands on. And best, of course, implies a hierarchy. And hierarchies mean death to the comprehensive ideal.
Years ago, as we twitchily began to confront the realities of our local city comprehensives, we attended what was euphemistically billed as an open morning at a London independent day school, but what turned out to be a rugby scrum of anxious parents pounding the hallways like predatory giants from Roald Dahl's BFG, flattening pupils against the walls and shrieking into teachers' faces about how to get their sons, some little more than babes in arms, into the school.
"Ah, the north London parent," the head observed mildly, from his observation post, high above the melee. "One of the most ferocious animals on this planet."
Parents are ferocious, willing, if need be, to trample on anything that gets in their children's way. Biology will always out, as Harriet Harman has found to her cost.
She, of course, claims it is all a question of Tory misrule. But imagine her local south London schools after 16 years of fabulous Labour funding and management. Would they really be good enough for a high-flying parent like herself? Or would their rag-tag intakes, and huge spread of ability and special needs, still have her putting her son on the train to somewhere more salubrious?
Because even if selection is made a hanging offence, there always will be somewhere more salubrious. The waves of parental choice will make sure of that - lifting a few schools to the high-achieving peaks; dropping others into social darkness.
And not just in the cities, either. Go to any area of the country, and parents will tell you instantly which are the good schools, and which to avoid like the plague.
When we decided to move out of London, and started to look around at the options, we found it harder to get into some comprehensives than into a high security prison. "Frankly", said one popular school in Chichester, "if you're not actually going to buy a house next to our front gate, there's really not much point you coming to look at us."
Initially we were looking at all kinds of schools, provided they were coeducational, and had a reasonably local intake, but it quickly became clear that the ones that we felt would suit our children best were all selective. It wasn't only their academic results, it was the facilities, the expectations, the sports and music, the lack of discipline problems, the pupils themselves - in short, the common culture. Or perhaps, in shorter still, hard though it is to admit, the exclusivity.
There was nothing actively wrong with the comprehensives we visited, it's just that other schools were better.
And herein lies the rub. For the comprehensive system to work properly, there must be no choice of any kind, otherwise parents like me - and Harriet Harman - will always be rubber-necking around at the opportunities outside.
Yet there never has been no choice. For those who can afford them, there have always been private schools. For those free to move, the grammar schools. Now there's the grant-maintained choice. And the city technology college choice. And even inside the comprehensive system, there's the working-the-system, or the moving-to-a-better-area choice.
I can count on the fingers of one hand the number of pro-comprehensive friends from pre-parenthood days (many paid-up members of the Labour party) who have actually put their children into comprehensives, and on half a hand, those who have done so using their neighbourhood school. When it comes to the parental crunch, it's almost always goodbye society at large, and hello self-interest.
The question is, how do we deal with that? To deny it is absurd. To denigrate it is equally absurd. To counter it with brave promises of "excellence for all" is not only unrealistic, but also misses the point.
Fudge is the easiest answer, but years of that have left us an absurd mish-mash of differing opportunities that no amount of emollient words from politicians of either Left or Right can smooth into a coherent whole.
In the light of this, the old 11-plus system seems almost attractive. At least it was honest, it judged the child not the parent, and everyone got a crack at it.
Or maybe what we need is selection at 14? Or maybe the real issue is not structural at all, but our total failure to respect and develop high standards of vocational and technical schooling?
Maybe if we ever managed to turn our pyramid model of school success into a whole Alpine range of achievement, then the poisoned chalice of school-type would lose much of its potency.
I don't know what the answer is, but I do know that, unlike Harriet Harman, every time I drop my son's grammar school uniform in the wash, I'll know that what has been a solution for us, has only been part of the problem for others.