Recently, while writing a book for parents about schools, I was haunted by a similar vision, although in mine there were three people coming down the mountain - three Lesotho children who, years ago when I lived in southern Africa, raced from the family kraal to flag down my car for a lift to school.

I thought about these children often as I wrestled with the book. It was supposed to tell parents how they could help their children succeed at school, but it often felt, as I worked on it, that this was a presumptuous thing for anyone to do, let alone someone who has never worked as a teacher and certainly can’t claim to have wildly successful children herself.

But, I reminded myself, it wasn’t a book about coming top of the class, but about how to help your child become a confident and happy learner.

And although I wasn’t a teacher, I had sat in on hundreds of classrooms, in all kinds of schools, and knew an awful lot about how children are not turning up in a good state of mind or body to do this.

As David Hart pointed out so graphically at the National Association of Head Teachers conference this week, far too many parents now send their children to school unfit and half-asleep, with their homework undone, and no clear rules about how to behave. The applause he got for this shows just how sick heads and teachers are of playing policeman and social worker to rude and unco-operative students. Recent published accounts from teachers Stuart Williams and Francis Gilbert have also lifted the lid on pupils’ often appalling classroom behaviour, and maybe the time has come for many more teachers to join them and tell it like it is.

Because parents need to think a lot more about school than just whether they can get their children into the “right” one, and how vigorously they can complain if all is not perfect once they get there.

They need to ask not only “how well is my child being taught?” but also “how well is he or she able to learn?”; to know the power they have to turn their children into great learners and to understand just how much more their children will get out of school if they do so - figures from the Department for Education and Skills show that children with supportive parents can do up to 10 per cent better in school than those without.

Not, though, by buying in tutors, hovering over homework, or rushing children into improving activities.

Much of my book concerns the very simplest things of family life - diet, sleep, exercise, play and conversation. It describes how children learn, what schools teach, and the everyday importance of things such as praise and boundaries. Surely stuff, I often thought doubtfully, that every parent in the land already knows? But the overwhelming evidence from schools is that this is not so, and if I ever doubted it I only had to look out of my window at the daily sight of children trailing to a local school - many of them late and lethargic, munching crisps and swigging fizzy drinks, spitting, swearing and loitering.

And I thought again about the three little Lesotho children running down the mountainside. They had come pouring out from a ragged-looking thatched rondavel halfway up the hill, but their fees had been scraped together from somewhere (school wasn’t free), their school shirts were Persil-white, their eyes were sparkling and clear, they were confident enough to stand in the road and wave me to a stop, and once in the car they were thrilled to show off their notebooks as they chattered like birds about their school day.

If I hadn’t come by, they said, they would have had to walk one hour to get there, but that didn’t matter. “You have to go to school. You have to have lessons and you have to listen to your teachers,” the littlest one said solemnly. “It is lucky for us to have a school that we can go to. If you don’t go to school, you can’t do anything, and all your life you will be poor.”

And when we got to the dilapidated tin-roofed hut that was this fount of all learning, they skipped off, eager as anything to start their day.

Hilary Wilce is an education journalist