Aldo Williams: Where the coffee's fresh but the teaching is stale

English summer, early on. Trees in full burst, grass at its greenest. If your school has grounds, this is the best time to show them off. Top private schools certainly have good grounds to show off, in more senses than one – look at those exam results – and so the open days come thick and fast now. It may be a nasty recession but times are still good for the top schools with interest up two- or more-fold.

Nearly all my career has been spent in comprehensives, but recently I went to the mountain top – taught for a term in one of our elite independent schools, often mentioned in dispatches. And the view was lovely: lovely grounds and buildings, lovely timetable, lovely pupils, lovely the provision of everything a teacher might want from fresh coffee to free lunch in a full-hour break.

One day the tennis courts were being power washed; the next the cricket square was having its third cut of the week, the nets erected for the arrival of a county coach. Suddenly, there were new plantings in the flower beds.

My comprehensive had tennis courts that were a bit battered, often littered, occasionally swept. There was a cricket wicket but not much interest from the staff and the grass rarely short enough for a game – not that there were ever many. But this doesn't surprise you.

Lessons were different in the public school. Pupils politely attentive; never any misbehaviour that couldn't be corrected with a glance or stare or, with the really tough classes, a slight raising of the voice. And I get a "Thank you" from each one of the 15 as they leave the room. Teaching days may be long, 5pm plus, but no lesson leaves you emotionally drained before the next 30 pile in. And with more free periods, a better pay scale, shorter terms and a real sense that the school values you – well there just aren't enough public schools to go round, are there? But there can be haze on mountain tops, and clouds.

I'm hazy about the quality of the teaching. If your pupils are hard-working and chosen to be, if not the brightest, then certainly not the dimmest, you don't need particularly good teaching to get great results. Cover the syllabus thoroughly and the pupils do the rest. Two staff from my comprehensive had gone to that school in the past few years: one after presiding over a dying department (which his replacement was able to turn round) the other just gave up: "The kids – so unruly." Well, not that unruly actually, but state teaching does require some steel in the spine and that was rather lacking in this teacher. Head of subject now.

So there's haze – and something of a cloud. In his diaries John Rae, the headmaster of Westminster School, wrote in 1977: "Overall numbers in independent schools have risen but the press don't notice that this is because schools have filled empty beds with pupils from the Far East and seem determined to write about a public school 'boom'."

And now? I suspect there are more than a few top public schools that would be blocks of flats were it not for help from the East. And, yes, it feels odd. You are teaching in this quintessentially English institution but wander into the sixth form area at lunchtime and you feel well east of Greenwich.

I loved my time at the school. I enjoyed teaching and the staff's company. But work in a comprehensive with all its pressures and you feel you're giving your pupils a leg up to do better than their parents or at least to get qualified. It doesn't feel like that when you know most pupils are cushioned by wealth.

The writer is a former teacher at a comprehensive school