The Association of Teachers and Lecturers said children were under "huge pressure" to buy brands.
The teachers' survey claims children are strongly aware of brands and logos, but pay little attention to the green or ethical values of products.
Brands are more influential to children than their own friends, the study says.
The study from the ATL teachers' union warns that children are under excessive commercial pressure to be seen buying and wearing fashionable brands.
The union's general secretary, Mary Bousted, says that "children are suffering the consequences" from advertising that targets youngsters.
"It is incredibly sad to hear how many youngsters are bullied or isolated for not having the same clothes or accessories as their classmates," said Dr Bousted.
A survey examined the experiences of 380 teachers in how brand-awareness was experienced by children in the playground.
"A lot of advertising companies blatantly target children without any consideration for the parents of those children," said Ann Seddon from Manor Field Infant school in Hampshire.
"They need to be up-to-date, otherwise they get left out and have low self-esteem," says Sheila Bell, a teacher from Cumbria included in the survey.
