The statistics were a snapshot of data collected as part of the National Child Measurement Programme, a nationwide survey of children's weight in reception and year 6, commissioned by the Department of Health.
The figures are not due until spring, but ten primary care trusts released them under the Freedom of Information Act.
The Isle of Wight had almost 30 per cent of children starting school overweight or obese. In Suffolk, and in Bath and north-east Somerset, 23 per cent of reception year pupils were overweight.
The new target states that by 2020, child obesity should be reduced to year 2000 levels.
Tam Fry of the National Obesity Forum said, 'The Government has shifted the goalposts. They need to refocus and look at the prevention of obesity, starting with pre-school. There are things they could do tomorrow that would have a significant impact.'
A DoH spokesperson said, 'When we set the 2004 target, we knew this would be a challenge; obesity is a global problem akin to climate change. We have reconsidered the position in the light of emerging evidence and have concluded that moving to this new ambition is the right thing to do.'
The Foresight report on obesity due later this week is expected to say that half of primary school boys and 20 per cent of girls will be obese by 2050.