Hi. I'm a parent. How will you treat my child?

One of the abiding legacies of the culture of parental choice, first introduced by the Conservative government in the late Eighties, is that parents now expect, and demand, easily accessible information from schools they are considering for their children. This includes not only league tables, annual reports and prospectuses, but opportunities to see the school in action on open days.

For independent schools, the open day has become a key part of the armoury in wooing prospective parents. Whereas 10 years ago, open days were rather ad hoc affairs organised only by some schools, and dependent on the keenness of one or two members of staff, now almost every independent school has at least one open day a year. Many schools employ marketing specialists to ensure that the open day goes with a bang.

"For parents, an open day is a good way of seeing a school and taking the temperature – without the commitment of going into who you are, and your child's history," says Rosellen Mates, development director at Frensham Heights, a co-educational boarding school near Farnham, in Surrey. "It is a semi-anonymous way of finding out about a school, and is particularly useful for parents exploring the independent sector for the first time."

Schools have responded to increasing parental demands for information by adopting a more professional approach to the open day, says Dick Davison of theIndependent Schools Council information service. "The open day has become more systematic, so that the school presents itself as a coherent whole," he says. "The old five-minute chat by the head is now more likely to take the form of a question and answer session with parents, and there is also more planned participation by the pupils."

In the past, parents considering independent schools in the Oxford area, for instance, would have found out about them by attending the ISCis exhibition. Now, however, parents want to see the schools for themselves – and the exhibition ceased two years ago.

Headington School for girls, in Oxford, runs an annual open day on a Saturday morning in October, which is promoted on its website and in its prospectus. For a couple of hours, parents tour the school and its grounds, witnessing "normal" lessons going on, as well as musical, dramatic and sporting displays – the kinds of extra-curricular activities that many independent schools pride themselves on. About two thirds of these parents are prospective, and the majority of them are considering secondary schools two to three years in advance. "Parents take the open day much more seriously now," says Laura Douglas, marketing manager for Headington School. "As schools give out more information, so parents ask more questions – and that's good, because we like parents to be involved with their children's education."

Some open days will be more highly stage-managed than others. Some schools prefer to have more frequent, smaller-scale open days, and to keep them more informal. Schools may follow up open days with questionnaires, to keep track of possible "clients". They also recognise that although important, the open day is not sufficient for some, and schools generally encourage a second – probably one-to-one – visit, for serious applicants.

Dulwich College for boys, in south London, now involves all staff in open days, organises more active demonstrations, with more pupil participation, and shows parents round in groups of five, rather than 20 as in the past.

"We can't rest on our laurels – or our reputation," says Simon Northcote-Green, the deputy master. "Parents are more demanding in terms of what they're looking for, and armed with more knowledge. We've become more open than we used to be, and more open to criticism. We have to listen more than we used to, to what the clients are feeling."

Cheltenham Ladies College not only organises 10 open days a year – each for about 30 families, who have requested visits – and "taster" evenings or weekends for prospective day girls and boarders, but also lays on an annual fun day of learning for all the family. On the May bank holiday each year, 10-year-old girls join the younger classes, while their parents pitch in with A-level economics or GCSE Spanish. "It's a sell-out," says Vicky Tuck, the principal. "It gives parents a real insight into the quality of teaching and the climate in the classroom."

Many parents considering an independent school will take for granted good exam results, decent facilities and small classes. But the open day also gives them the chance to get a feel for that indefinable quality of a school – the ethos, the atmosphere, the relationships between pupils and teachers.

"What parents seem increasingly concerned about when they visit a school is whether or not their child will be happy," says Jane Peake, development director at Bootham School in York, a co-educational Quaker school. "It's all part of the consumer age: individual choices for individual needs."