CHILDREN have grown too big for their school chairs, a survey of 750 schools revealed.Teachers said "desk and chair sizes were often inappropriate".
It is understood the Education Department has been taking orders for custom-sized chairs.
Paediatric dietician Susie Burrell said children who were overweight often didn't carry obvious fat but instead looked older than their age.
She said children risked weight problems or diseases such as diabetes and fatty liver.
She said parents should check if their children's waist measurement at the belly button was less than half their height.
Having to wear clothing more than two sizes bigger than their age group could also indicate a problem.
A Teachers Federation spokesman said it was also common for students in Years 5 and 6 to be taught in Year 3 classrooms with small chairs.
The Education Department said schools were running healthy eating programs.
"The department takes the issue of childhood obesity seriously and works with a number of agencies to address the issue," a spokesman said.
"We have a number of initiatives to support school communities as well as promote healthy eating."
He said parents needed to enforce the message about healthy eating and a healthy lifestyle at home.