Lessons in cookery and healthy eating should have been made compulsory in a shake-up of the national curriculum, food technology teachers have said.
Concern about pupils' nutrition has been headline news
The comments come as the Qualifications and Curriculum Authority is about to publish plans to revise what 11 to 14-year-olds are expected to study.
Education Secretary Alan Johnson says he wants them cooking from scratch.
But teaching representatives say if the government were serious about fighting obesity, classes would be obligatory.
Louise Davies, deputy chief executive of the body which represents "food technology" teachers, the Design and Technology Association, said youngsters needed to be given the tools to make changes to their lifestyles.
"It's not simply about knowing you have to eat five portions of fruit and vegetables a day - you need to know how to turn them into healthy meals.
"If the government was really serious about battling obesity, then food technology classes would be made compulsory."
She added: "What they have done is emphasise that food technology classes should be about practical cooking, but schools can still choose not to bother to do the classes anyway.
"And a lot of schools, mainly boys' schools, don't bother."
Ms Davies explained that giving children "an entitlement" to attend cookery classes meant schools could provide them in after school clubs, at the weekend or in summer schools.
"There's no point in changing school meals and telling children to eat healthily unless we get the children to change the behaviour as well.
"It's about empowering children to change their diets."
Announcing the plans to change the curriculum, Mr Johnson said cooking was an essential life skill and a vital part of tackling obesity.
"I want kids to roll their sleeves up and actually get to grips with preparing simple healthy meals from scratch.
"Young people are interested in cooking and with role models like Jamie Oliver on our TV screens there is no reason why we can't get more kids cooking both in school and out of school."
But Ms Davies said Mr Johnson had given a clear steer to the QCA not to make the subject compulsory when he announced in the autumn that children would be offered rather than given cookery lessons.
Soon after a letter signed by nearly 50 health and educational organisations urged Mr Johnson to make such classes compulsory.
Other changes to the curriculum, designed to give teachers greater flexibility to teach what is relevant to their pupils, have been welcomed by teachers.
Plans to make the study of slavery and its abolition compulsory in history lessons at Key Stage 3 are also expected to be announced.
Chair of secondary education at the Historical Association Heather Scott said: "It's compulsory to teach history from 1066 to the present day.
"How can you do that effectively without teaching world wars one and two, the Holocaust and slavery.
"It's such a key part of British history and a good teacher will be doing that anyway."
The extra flexibility in the curriculum would allow teachers to play to their specialisms, she added, and make use of their own material in class.
Plans to put climate change and sustainable development at the heart of geography teaching have also been welcomed by teachers.
Head of education at the Royal Geographical Society, Steve Brace, said teaching climate change fits in with the idea of making geography lessons relevant to pupils.
He said: "What geography does is it makes young people investigate the connections between people, places and environments.
"Studying climate change allows pupils to understand the key scientific processes, explore how it will impact on us and gives them the skills to live more sustainably in their own lives."