By Simon Cox Presenter, BBC Radio 4: The Truth About School League Tables

Richard Wallis receives his award for outstanding headship

This week has been a good one for Sandwich Technical School in Kent.

Its head teacher, Richard Wallis, was named best in the country at the profession's annual awards.

Its GCSE-level results are going up, as is its place in the league tables.

But look closer and you see that the number of pupils who attained good grades in English and maths GCSEs was lower in 2004 than in 2001.

How could a school be improving while simultaneously getting worse at the basics?

A teacher from a Midlands comprehensive, who did not want to be identified for fear of damaging his school, told us: "From what I've seen, schools use the GNVQ to boost their results ... the league tables are a con because they're a meaningless number - a statistic that can be twisted."

It is a claim sceptics have repeatedly made but for the first time we had the figures to prove it.

Leaking classroom

We had obtained the results for every school in England for the percentage of pupils with five good GCSEs including English and maths.

This is the new measure for league tables from 2007. It means bad news for hundreds of schools that have been improving in the league.

The North School in Ashford, Kent, is one of them.

Its buildings badly need a makeover - some are rumoured to have been built by Italian prisoners of war - but it is one of the most improved schools in the country.

In a leaking classroom in the science block I found out how they had done it. Pupils here are taking the GNVQ in science.

Fred, 14, is one of them.

"It's not what you call hard work but it's still work," he said.

His friend Ben adds that it is worth four GCSEs.

They also do the GNVQ in information technology and last year they got a 100% pass rate.

'It's a scam'

The pupils like them, the schools like them - but should they really be equivalent to four good GCSEs?

Chris Woodhead, the former chief inspector of England's schools, does not think so.

"It is a scam that's admitted even by the schools and the teachers that are entering their children for these qualifications," he told me.

Not surprisingly that is not how the North's headmaster, Simon Murphy, sees things.

"To me that doesn't matter. To me the important thing is the whole agenda for raising standards."

But it matters to their place in the league tables. Under the new measure including English and maths, the school's GCSEs results are cut in half.

'Playing the system'

The North school is improving - just not as much as the league tables suggest.

That is not the case for hundreds of schools in England.

According to the figures we obtained, more than 300 mainstream state schools went up the league tables while their results for English and maths went down.

That is one in six improving schools.

The teacher who admits his school used the GNVQ to go up the league table said these figures would come as no surprise to many senior staff.

"One of the deputy heads I spoke to did comment that schools don't make the system we work in, we just play the system."

The government has these figures, so do individual schools, the only people who don't are the parents - until now.