The NHS figures are based on body mass index
One in five of all primary one pupils in Scotland are overweight - the lowest proportion since 2000-01, new statistics have revealed.
Figures for 2008-09 showed that 19.8% of primary ones weighed too much, but the figure is down slightly from the previous year when 20% were overweight.
Opposition parties accused the government of breaking promises.
But the Scottish government welcomed the "downward trend" and said action had been taken to reduce obesity.
The figures are based on body mass index (BMI), which uses a height and weight formula.
Across Scotland, 19.8% of primary one pupils were classed as overweight, while 8% of primary ones were obese and 3.9% severely obese.
But in the country's most deprived areas, 21.2% of primary ones were overweight, 9.2% were obese and 4.7% were severely obese.
In the wealthiest areas 16.7% of primary one children were overweight, 6.2% obese and 2.6% severely obese.
Childhood obesity can lead to a number of health problems in later life, such as heart disease, diabetes, osteoarthritis, back pain and cancer.
The Lib Dem health spokesman Ross Finnie described childhood obesity as a "a ticking time bomb" and said that, as of September, only a third of primary schools had hit the government's target for physical education.
"Unless ministers make tackling childhood obesity a key priority, the progress that Scotland has made on cutting heart disease, strokes and cancer could be undone," he said.
Mary Scanlon, the Conservative health spokeswoman, described the figures as "very worrying" for a country the size of Scotland.
"The promise of two hours of quality physical education was not met by the previous Labour-Lib Dem executive nor has it been by the SNP government," she said.
A Scottish government spokesman said action had been taken to reduce the number of obese children and increase the level of physical activity undertaken by people in Scotland, citing the Healthy Eating, Active Living action plan.
But he added: "We remain concerned that the level of obesity is still too high and we must continue to take action to improve the diet and increase physical activity levels of children to see overweight and obesity levels continue to drop."