Encouraging children to eat more "junk food" through school-based promotions is "frightening", teachers have heard.
The National Union of Teachers (NUT) conference in Harrogate, North Yorkshire, was told that campaigns by companies such as the confectioner Cadbury and the crisp-maker Walkers would have a detrimental effect on children's health.
The union voted to sponsor teaching materials which help children "question" the messages of advertising and to campaign for a minimum of 90 minutes of physical exercise per week for all children.
Ian Thompson, a teacher from Gloucestershire, said: "It is nothing more than marketing to our children in the name of education.
"It involves selling saturated rubbish to the people we teach."
Cadbury, which is running a school sports initiative, came in for particular criticism.
It is offering to spend £9m on equipment if pupils and parents, through schools, collect enough tokens from its sweets.
Walkers, which has a Free Books For Schools campaign, was also accused of using its promotion for commercial ends.
Of the Cadbury campaign, Pete Bishop of the NUT executive said: "There will be 160 million chocolate bars carrying tokens.
"That's a frightening prospect for schools."
Cadbury says the number of calories consumed by children has not risen, but exercise levels have dropped.
This, it says, is the problem its initiative is targeting.
But Chris Wilkin, a teacher from Coventry, told the conference: "It is difficult for children not to participate, as parents and children are under pressure to collect vouchers.
"The companies could give the schools money through the setting up of community funds.
"Schools must be better funded in the first place, so we don't have to go to companies."
All advertising aimed at children under the age of 12 was banned in Sweden in 1991.
The conference noted a Food Commission report from 2000 which found that, for every healthy product targeted at children, 10 more were "nutritional disasters".
Nigel Baker, a teacher from Birmingham, said: "Let's defend and reclaim our children's chance to develop as healthy and tolerant individuals and push back the tide of commercialisation."
The conference unanimously passed the motion condemning the commercialisation of schools.