At this time of year, sixth form common rooms are full of anxious-looking students clutching prospectuses and the dreaded Ucas form for university entrance. It is not surprising that they are so daunted. The average teenager has 4,000 characters in which to explain their achievements to an admissions tutor in some dim and distant university.

Some young people may have been for a look at the university and its environs, but a few hours examining the facilities, and attending the odd introductory lecture, is hardly enough preparation to write one of the most important documents of their career to date, the personal statement.

Most university tutors do understand how arduous the task is. When quizzed, they give a laugh, and say: "Do not, tell me that you like mountain climbing, or that you've got your Duke of Edinburgh award. Tell me why you're passionate about the subject you're going to study."

This, however, is to little avail. Many students, perhaps the majority, apply to study more than one subject on their Ucas form. Having carefully read the prospectuses, and been on the said open days, a student might want to do English at one place, film and literature at two others and American studies with film, at a fourth and fifth. To show a love of English alone on their personal statement would be a mistake. To introduce film or American studies might be too much.

Schools and colleges must take some of the blame for young people over-emphasizing extra-curricular pursuits on the personal statement. They are keen that young people have interests that are broader than simply the academic, which can be summed up neatly in an exam certificate. They are anxious that their teenage charges be seen as the responsible citizens of the future. That is why they push them into listing their captaincy of the football team or their Young Enterprise award. Students put on fashion shows for charity, have global awareness days in the local community, and raise money for Children in Need. All this, their teachers claim, should go on the form. The question is where, and in how much detail? Too much of the personal makes the application sound anecdotal, too little makes the student sound like a drone.

And then there are the predicted grades. Most universities do not bother to read the applications of students who are expected to fall short of the requirements for the course. Teachers making the predictions would thus seem to have a considerable say in whether or not a candidate gets in.

On top of this, some schools, many of them independent, are better at getting pupils in to the top universities than others. So, if you apply from Westminster School you are far more likely to get in to the university of your choice than if you go to a comprehensive in Huddersfield.

There is something about the way the form is filled in at comprehensives – both the personal statement from the young person and the supporting comments of the teacher – that makes it stand less of a chance than applications from independent schools. But nobody seems to specify exactly why this is, or how the comprehensives could improve their performance.

Class, it seems, still plays a key role in the applications process. This finding is most worrying of all. At one school, a head of department was so demoralised by seeing hordes of excellent, A-grade students being denied interviews, let alone getting in, that he was compelled to write to the University of Warwick. He wanted to know just what it was about what he was writing, and what his candidates were writing, that made so many of his students end up on the reject pile. Who knows if they deigned to respond? Most universities no longer interview applicants on the grounds that it would disadvantage young people who are less articulate and polished in their performance than others.

There was particular concern that independent schools students might be more groomed than, for example, students from inner- city comprehensives. So, the interview was replaced by the personal statement. But it appears a bias remains. A university tutor may subconsciously choose someone like themselves, rather than the best qualified. Something is wrong when enthusiasm for the subject and A-grades are not enough. Today's students are right to be anxious about their personal statement.

The writer is senior lecturer in education at King's College, London