One in three children in the final year of primary school in England is overweight or obese, figures show.
The 2011-12 data, from the National Child Measurement Programme, which involves over one million pupils, is a slight increase on the previous year.
The figures released by the Health and Social Care Information Centre also showed more than a fifth of children in reception are overweight or obese.
Rates in the poorest areas were nearly twice as high as the richest.
The programme has been running for six years now - and figures from previous years have given hope child obesity may be levelling off as there has been little or no change on many counts.
For children in year six - the final year of school - who are aged 10 and 11 there has been a small rise.
The proportion of obese and overweight children in year six was 33.9%, up from 33.4% last year.
Taking just the obese - those with the most serious weight problems - the figure stood at 19.2%, up from 19%.
'Best start in life'
By comparison 22.6% of children in reception - aged four and five - were obese or overweight. That was exactly the same as the 2010-11 data.
When just the obese are taken into account, the rate rose ever so slightly from 9.4% to 9.5%.
But despite there being no large rises in the numbers, campaigners said there was still much to be done.
Tam Fry, of the National Obesity Forum, said the government needed to focus on improving access to exercise as well as making healthy food more affordable for the poorest.
"The government has totally let down a raft of children," he added.
And Diane Abbott, Labour's shadow public health minister, accused the government of a "total lack of interest" in the issue.
But Public Health Minister Anna Soubry said the government was taking action.
She pointed out that through the responsibility deal, whereby food producers are making their products healthier, and via the Change4Life programme, which supports local projects that promote healthy lifestyles, progress was being made.
"Being overweight can do serious damage to our health so we must reduce levels in children to give them the best start in life."