Coca-Cola & Schweppes Beverages has targeted heads in selected regions to promote the machines as 'the free and easy way to generate extra income for your school'.
The company declined to say how many machines have been installed in primary schools, but claims on its promotional literature that 'many more head teachers take up our free offer every week'. It promises payments which 'could easily add up to as much as pounds 400. Very often it is much more.'
The British Dental Association has written to its district dental officers asking them to alert headteachers to the Coca- Cola promotion and discourage them from taking it up.
Bryan Harvey, scientific adviser to the association, said: 'Heads should ask themselves whether they should be promoting something which is known to be harmful to children.
'If you put sugary, soft drinks on the school site, children will drink them more often during the day, causing their teeth to be continually bathed in sugar. This is known to cause tooth decay.'
Michael Cartwright of the National Association of Headteachers said: 'It is a moral dilemma. It ought not to be necessary to sell Coca-Cola to raise the money you need to run a school, but we did not invent the market-place philosophy.'
Many schools, especially secondary schools, run tuckshops selling sugary food and drinks. But the Coca-Cola promotion is believed to be the first to target primary schools and to advertise the financial incentive to get headteachers' co-operation.
It raises the prospect of other companies - toy, record and computer games manufacturers, for example - using schools as retail outlets by offering a cut of takings.
However, some schools have found the machines were not as lucrative as they had hoped. The head of a south London primary school sent the machine back after finding it needed constant supervision. 'A kid would put money in and then another would walk past and press a button so the buyer would get the wrong drink.
'Or someone would put money in then discover they hadn't got the right change and go off to get it. Meanwhile someone else would insert the extra five pence and get the can. We didn't get as much money as we were led to expect and as that was the whole point we sent it back after six months.'
Leading article, page 21