Test purchasing is being rolled out across Scotland from May 1.
The Scottish Executive has decided to expand the scheme after last year's pilot in Fife was hailed a success.
In the off-trade, 16.8 per cent of drinks shop test purchases resulted in the sale of alcohol to a child, but Fife police said most licensed premises had responded positively even if they had failed the test.
Scottish health minister Andy Kerr said: "Communities across Scotland are blighted by the problems associated with under-age drinking, and rolling out test purchasing will give us a valuable tool in the fight against this.
"I know that the vast majority of retailers take their responsibility very seriously but we need to take action against the minority who sell alcohol without carrying out the proper checks."
The scheme will use 16-year-old volunteers and local authorities will work with police to determine which premises to target and when.
Unlike authorities in England and Wales, both successes and failures will be published.
The Scottish Executive is working on best practice guidelines, but has not confirmed whether it will, for example, permit volunteers to lie or use fake ID as has happened in England.
Fife findings show support for national ID card scheme
Drinks shops fared better than the on-trade in Fife's test purchase pilot, a summary report shows.
Of 573 test purchases, 98 (17 per cent) resulted in volunteers being sold alcohol, with 16.8 per cent of off-trade test purchases resulting in a sale, compared with 17.9 per cent in the on-trade.
Fife police commissioned preliminary interviews with 100 licensed premises, including 31 grocers, 12 supermarkets and five off-licences. Drinks retailers were more likely to say they had a great deal of knowledge of test-purchasing (46 per cent) than their counterparts in the on-trade (8 per cent). Shop managers were three times more likely to say they gave their staff a lot of training (46 per cent) compared to those based in the on-trade (15 per cent).
Most drinks shops supported test purchasing, alongside a national ID card scheme, as the best way of stopping alcohol sales to children.