In the most comprehensive study yet done on the matter, Penelope Leach has unlocked the secret of the terrible twos: toddlers are rotten, for sure; but those raised by their mothers, as opposed to other carers, are substantially less rotten. They are less "aggressive", less "compliant" and less "withdrawn".

There is some offset value there, surely? If children are withdrawn and compliant, you're unlikely to notice when they're aggressive. They're probably just off stabbing insects. Besides which, I have a problem believing the study, since the funniest - though least scientific - evidence I've heard on this was a mother writing in the New Yorker.

She says she gave up her job to look after her son, on the advice of research just such as Leach's, and the only difference she saw in his mental development at three years old was that all his friends were better at picking stuff up after themselves. I wish I could tell you her name, but sadly a prolonged career hiatus means she isn't at all famous.

Here are some things that have never been explained to me. First, does it matter if children develop late? Does it necessarily mean they won't develop eventually? (I was very late in learning to read. I blame my mother, of course. She was too busy doing prototype ball-busting.) Second, why, in these studies, is it always mothers versus all other carers? Why not one-on-one care versus group care? Surely that's the key difference between maternal and non-maternal toddler-tending, given that not all mothers are equally good at being mothers. Mainly, though, I want to know: what is the purpose of a study like this? Who does it help? Have you ever seen a study of the mental health of adults who work, set against those who don't? Or a paper on the incidence of cancer among people with jobs, compared with the jobless? Of course not - because it doesn't matter, ultimately, whether work depresses you or makes you ill. It is a given that you have to work, so academic inquiry into its effects is deemed void unless, of course, you are female, in which case you still have to work, but are also responsible for all the negative consequences that proceed from that.

It is important not to shoot the messenger, as I learned last week, huffing and puffing about the obstetric consultants who told women not to put off childbirth in favour of a career. We're not putting it off in favour of a career, I raged. These are just jobs, without which we cannot earn. To put them on hold we need active support - ergo, for every woman who defers there is a man deferring also. And yet when I met these doctors I realised their intentions were noble; they were simply pointing out biological facts. The twist - that women must try harder, must in some way defy the exigencies of the work-to-survive society - was added later, by people discussing the research. Likewise, Leach's study, which may stem from a desire to see government policy reversed, will be used as a stick to beat women who are already in a no-win situation. The New Labour line on this, let's not forget, is to get mothers back to work. The slogan is "making work work". It's meant to be witty wordplay; instead it just sounds like twice as much work.

The media psychologist Oliver James recently recalled a furious response to a piece he wrote stating that three-year-olds learned little from each other and were better off with their mothers. His reaction was a rather cavalier pop-psych shrug, in the manner of: "What does it say about your feelings, that you would be angry when someone simply tells you the truth?" Well, I'm angry for this very simple reason: you wouldn't tell someone in prison how bad it is for babies to be born to handcuffed mothers; you wouldn't tell someone on a desert island how bad it is for children to eat too much fish. Ask not whether it's true; ask whether it's helpful. Ask whether there's anything anyone can do.