Det går kanske att tolka studien som om pojkar tar större skada av föräldrars separationer än flickor. Ett svårsmält budskap och forskarna tvekar.

“We find no real relationship between parental input and girls’ achievement. It’s kind of like they are protected, in a sense. The parental input just becomes more relevant for the boys than for the girls.”

The findings were in no way intended to stigmatise single parents, she stressed. “It’s obviously a much more complicated picture. The only thing we’re trying to say – and we’re not the first ones to make this point – is that these families are very different in how much time they spend with their children, maybe because they have to spend more time at work. They don’t have to be malign reasons.

“But we’re not really going down that path. We’re documenting this fact, which is already fairly well accepted, and saying that, because this input matters so differentially for boys and girls, boys do particularly poorly in these families.”

Dylan Wiliam, emeritus professor of educational assessment at London University’s Institute of Education, said the study added to “a growing literature of things which explain exactly how disadvantage impacts children”.

“Obviously, home background makes a difference to all kids, but it seems to make more difference to boys than it does to girls,” he said. “It could be that girls are more resilient, but then also less able to take advantage of the very strong effects of positive parenting.”

The gender gap was a quite vexed area of educational research, he added. “It’s something people are quite sensitive about, and it can be hard to discuss in a sensible way, without just saying, ‘Well, they’re just boys.’ And the other thing people point out is that when boys outperformed girls no one worried about it.”

Den sista åsikten är vanlig i Sverige. Jag menar fortfarande att det är en mycket obehaglig form av revanschism.