Official Scottish Government statistics reveal that despite regular warnings about the problem and scale of underage drinking, just three people under 18 were convicted of buying alcoholic drinks between 2010 and 2013, with no convictions at all in the first of those years.
In the same three-year period almost 160 alleged offences involving under-18s were reported to prosecutors. Buying drink underage carries the maximum sanction of a £5000 fine and three months' imprisonment.
Figures also show convictions of those aged 18 and over for illegally buying alcohol for under-18s soared to almost 200 in the three-year period.
The Scottish Government said it was committed to protecting young people from alcohol-related harm and was introducing legislation to allow police more powers to break up youth drinking dens.
But lawyers and trade groups said enforcement of existing legislation would send out a message on the consequences of breaking the law, with currently only businesses punished for being duped.
Scottish Conservative leader Ruth Davidson asked for the figures from Justice Secretary Kenny MacAskill. She said: "We know that there are problems in Scotland with underage drinking and it is important to know whether the sanctions that exist to prevent it are effective.
"If the law isn't keeping up with the problem, then perhaps it needs to be reviewed."
Alcohol law expert Jack Cummins, who advised the Government on licensing policy, said: "The figures indicate that there's a prosecution policy of giving immunity to under-18s who manage to buy alcohol by tricking conscientious retailers.
"Prosecutors ought to play their part and support responsible businesses by sending a message to these youngsters that they can expect to face the consequences."
A recent High Court case is cited as evidence of willingness to prosecute businesses rather than under-18s. Two girls aged just under 18 conned staff at an Aberdeen nightclub into selling them drink. Both gave Crown evidence against the licensee, whose conviction was quashed on appeal.
Paul Waterson, chief executive of the Scottish Licensed Trade Association, said the statistics confirmed fears that rigorous law enforcement would impact on the trade and not the perpetrator.
He added: "It's ridiculous that people approaching with forged documents face no action yet the operator who has been duped does, and risks losing their livelihood."
The Scottish Grocers' Federation said: "No one wants to criminalise young people but the law has to be enforced effectively and applied to anyone who commits an offence."
In his response to Ms Davidson, Mr MacAskill said there were "many different forms of action that the procurator-fiscal can take, including referral to the Children's Reporter, fiscal fines, the imposition of fiscal work orders and other alternatives to prosecution".
Chief Superintendent Helen Swann of Police Scotland's licensing division said: "There are other very effective measures which we can and do adopt which robustly address underage drinking without criminalising our young people.
"Police Scotland's focus when applying licensing legislation is to tackle those who sell and supply alcohol to under-18s whilst seizing alcohol from those underage."
No-one from the Crown Office was available to comment.