Pupils' weight and fitness details are being added to school reports in the US, in an effort to reduce obesity levels.
US children are eating too much fast food
The scheme, being piloted in Boston, has already made parents twice as likely to set weight-control programmes for their children, a study suggests.
The US government recently revealed 15% of six to 19 year olds were severely overweight or obese - double the rate 20 years ago.
Health campaigners have blamed an increasingly fatty, fast food-based diet and a reduction in children's activity levels.
'We need to think'
Robert McGowan, head of physical education in Boston, said: "Parents who received health and fitness report cards were almost twice as likely to know or acknowledge that
their child was actually overweight than those parents who
did not get a report card."
The rise in childhood obesity is believed to have caused higher rates of diseases, such as diabetes, in adulthood.
Last week, the American Academy of Pediatrics urged doctors to measure young people's weights.
Paediatrician Dr Frederick Rivara said: "We really need to think about interventions during childhood and adolescence, not only to prevent childhood obesity but also to prevent adult obesity."
The Boston study, published in Archives of Pediatrics and Adolescent Medicine, looked at 1,396 students at four elementary schools in 2001-2.
Health report cards were sent at the end of the academic year to 481 parents, including those with normal weight children.
Afterwards, 42% of parents of those deemed overweight said they were planning to set up a programme of physical activities.
Meanwhile, 25% said they would consult a doctor and 19% said they would improve their children's diets.
Among parents of overweight pupils who did not receive cards, just 13% reported doing any of those activities.
While some children were uncomfortable with the report-card programme, most parents responded favourably, the study found.
The scheme has been expanded to include 12 schools.