Natalie Haynes: So much better when the schools fed us caviar for lunch

The thing is that, as my grandmother once observed after she'd refused to splash out on the pest control man, and instead witnessed the spectacle of her neighbour crushing a rat to death with a shovel, you get what you pay for.

Private companies vie with each other to provide public services at ever lower costs, and school meals is just the latest in a run of scandals that necessarily emanate from cheapness.

In the bad old days, as I remember them, school dinners were provided by the school, and therefore the LEA was probably involved somewhere to make sure they didn't give us cat food. Or that if they did, they at least had the decency to pretend it was shepherd's pie.

But then it became clear that schools were wasting our money on dinners for pupils. I'm not quite sure where this belief came from: try as I might, I can't remember a tabloid scoop featuring a headteacher feeding his pupils on caviar and quails' eggs. But nonetheless, we somehow all came to believe that dinner ladies were the ladle-wielding face of vulture capitalism, and contracts were offered to private companies instead.

Oddly enough, even though the public sector is renowned for doing nothing but sitting on its collective backside, burning tenners to keep warm, it turns out that those private companies have not been able to provide school meals more cheaply: 62 per cent of teachers surveyed by the Association of Teachers and Lecturers said that meal prices had risen by up to 50p a day.

This is hardly surprising given the increasing costs of many basic foodstuffs in the past few years.

But private providers don't want to admit this, and raise the cost of their bids, because if they raise the bid cost, they might lose out to a cheaper rival. So they have taken a rather sneakier route, and cut the amount of food they provide to each school instead. It's simple maths, really. The most expensive part of a school-meals contract is providing school meals. Cut back on those, and your costs really will go right down.

Sure, there will be reports of primary school children going hungry with the new tiny portion sizes, and the odd scare story of even the tiny portions being too few for the number of children who need a school lunch on a particular day.

But what better way to encourage children to really want that lunch than by creating scarcity? It's market forces at work.

And who can deny the arithmetic, apart from an eight-year old who's too hungry after lunch to focus on his sums?