Organising pupils into sets by ability is common sense. Most teachers agree with that.
Teaching mixed-ability classes can be too much like an impossible balancing act. Pitch the lesson too high and the pupils who struggle in your subject will fall even further behind. Go for the lowest common denominator and you will fail to stretch your brighter students, and they will get bored. Somewhere along the line you will probably miss out the pupils in the middle, too. It is so much easier to plan for a class of roughly the same ability.
Pupils often see it as common sense as well: there is a lesser risk of looking like a swot or a thicko in front of your classmates if they are at the same level as you.
Parents like it, too. And politicians? Not only do they agree with teachers, they even agree with each other. Labour promised more streaming when it came to power in 1997. The current education secretary, Conservative Michael Gove, has pledged to push it even further, describing it as the "only solution" that would ensure the "brightest pupils continue to be stretched at the same time as pupils who might be struggling are given extra support".
So most people agree that setting is common sense (and, for the very little that it is worth, my gut instinct would be to favour it, too). But the problem with common sense is that it is not always right. After all, common sense suggests the earth is flat, and that heavy objects fall faster than lighter ones. Sometimes we need to think more scientifically.
The research in this week's report (pages 4-7) suggests that, contrary to popular belief, setting could be causing more harm than good. The findings - not just from the UK, but from academics in other countries - indicate negative impacts on those of middle and lower abilities. Meanwhile, the benefits to high achievers may have been exaggerated, as they can gain academically from explaining concepts to classmates.
This may not convince schools to drop setting altogether. But it should cause pause for thought. Schools at least need to ask themselves what they believe: is setting really helping all their pupils - or is it just making work easier for their teachers?