Setting can avoid pupils being bored or struggling in a class

Figures released by Ofsted inspectors show only 37% of classes observed in England in 2003 were set by ability - down from 39% in 2001.

Tony Blair said in 1999 that schools needed to "take account of different abilities, for example by setting".

Ability sets are most common in maths and science, the Ofsted figures showed.

Setting 'encouraged'

Setting - grouping children by ability in each subject - is different from streaming, where children are put in one ability group across all subjects.

Streaming was favoured in old secondary modern schools, but is no longer thought to be commonly used.

In 2003 - the most recent figures available - over 80% of maths classes were taught in sets at key stage 3 and key stage 4 (ages 14 and 16).

But its use is low in music (7%), history (29%) and religious education (23%).

However, setting has increased in modern languages and English - up to 62% and 51% respectively.

Mr Blair has said that extending setting would be preferable to increasing the number of selective or grammar schools.

Current advice from the Department for Education and Skills is that setting does raise standards and engages pupils with their own learning, but it is up to schools to decide how and when to group and set pupils.

"The significant majority of maths, English, science and modern foreign language lessons in secondary schools, already organised by setting," a spokesman said.

"And putting children into different ability groups within class is commonplace in primary schools.

�We have encouraged schools to use setting since 1997, and will continue to do so. Our White Paper sets out proposals to encourage even more schools to adopt setting, with best practice research to be published shortly.�

'No stigma'

A spokeswoman for the National Union of Teachers said she believed setting was "prevalent in most secondary schools", and that many primary schools used it for their older children.

She said it was a useful way of ensuring pupils got the appropriate teaching and support for their needs, and it allowed children the flexibility to develop strengths in particular subjects.

Opponents of setting say that those placed in lower sets can feel demoralised.

But John Hunter, deputy head teacher of St Marylebone CofE School in central London, says many teachers find it difficult to pitch a lesson at the right level in a class where abilities vary greatly.

"It's incredibly difficult to juggle a lesson plan so skilfully that you challenge every individual within a class."

The Church of England school in central London has a mixed ability intake but at least 50% of have a faith - not necessarily Christian.

It now places pupils in ability sets in most subjects.

School results have improved in recent years and there are clear advantages of setting for both pupils and staff, Mr Hunter says.

"Teachers can teach more effectively, target support to those less able and stretch those at the top."

And there is no stigma attached to being in the "bottom" set, according to Mr Hunter.

"We haven't dropped our expected standards for those in the lower sets," he says, "and some pupils do move up through sets.

"We don't have a system where we set and forget.

"If I thought for a minute we were stigmatising pupils we would rethink."