Picture this: it's Year 8 French, the bottom set. They're a lively bunch - keenly intelligent, witty, either co-operative or ready to fight, depending on how they perceive me today. We're doing "the family" and it's a nice little lesson. I did it yesterday with the top set, who were smiling, docile, confident kids without any obvious body-piercing.
I talk a bit. They try to guess what I'm saying. We watch a snatch of video and do a task on tape. They repeat the words and then draw and label their own families. The fragrant girls in the top set love this as they work through mere and pere to soeur and frere and other relatives.
But today the bottom set want to know non-nuclear family vocabulary. "Sir, what's French for stepbrother?" "My mum's boyfriend?" "Half-sister?" "Do I have to put both my dads in the picture, Sir?"
The stresses and strains of not having enough money have fractured these children's families to the point where many of them can't remember which house they're supposed to go to at the end of the school day. But "less able" is the category used to define them.
It has a fatalistic ring - what can we do beyond the most basic? The label depersonalises them. Similarly, a child who has basic needs in terms of housing and parenting is categorised as having "special needs". We try to remedy the fact that his current stepfather is on permanent night-shift, or that his mother is chronically depressed, by giving him extra literacy lessons. Always the symptoms, never the disease.
I applied for a job in a school outside my area. After chatting to the head's secretary about the post, I asked as casually as I could: "Am I right that most children at your school come from, er, middle-class backgrounds?" She was quite unfazed and replied enthusiastically: "Oh, by no means. We have children of all abilities here."
It was an unguarded moment, but conflation of "ability" and "social class" is standard in education. We have known for a long time that school, with its dominant ethos of middle-class femininity, has failed to reach working-class children, especially boys. But our response has been a cynical one.
Those who fail to relate to school are termed "less able", while others are "able" or "gifted and talented". The fact that these labels fit quite neatly, like a template, over categories of social class is studiously ignored.
Politicians tell us that, as teachers, it's up to us to raise standards. We must ensure that all pupils, regardless of ability, must have a chance to achieve. The Government will have us believe that we can overturn a class system entrenched since the Norman Conquest if we make our lessons more inspiring, make more effort to reach the less able.
This idea that society is formed by its schools is very much at odds with the obvious truth that schools are simply mirrors of the society that creates them. But if this latter view became widely accepted, then who could we blame for society's failures? Not teachers any longer. It's a dangerous thought.
So what's the answer? For a start, we could stop talking about ability all the time - ability has nothing to do with it. As somebody once said: "It's the economy, stupid."
Tim Jones teaches French and German at Braunton school and community college, an 11-16 state comprehensive in north Devon