The OECD has warned that "far too many students" around the world are struggling to understand money matters.
Around one in four students are unable to make even simple decisions when it comes to everyday spending, its newly-published study of the financial literacy in 15 countries has revealed.
Only one in 10, meanwhile, have a grasp of complex issues such as income tax.
The knowledge and skills of 48,000 15-year-olds from nations including the US, Belgium, Italy and Spain (Ireland was not included) were evaluated in the test, which looked at everything from bank accounts and debit cards to the workings of loan interest rates and mobile phone payment plans.
Some 64% of teens earn money from some type of work and 59% receive an allowance, meaning that they are already in a position where it would be beneficial to be financially savvy.
A further 56% of the teens have a bank account, while 19% having a prepaid debit card.
Despite this, less than one in three (31%) were found to have the skills to actually manage a bank account.
OECD secretary-general Angel Gurría said at the launch of the report in Paris:
"Young people today face more challenging financial choices and more uncertain economic and job prospects given rapid socioeconomic transformation, digitalisation and technological change; however, they often lack the education, training and tools to make informed decisions on matters affecting their financial wellbeing.
"This makes it even more important that we step up our global efforts to help improve the essential life skill of financial literacy."
The study was undertaken in 2015 as part of the OECD's Programme for International Student Assessment (PISA).
Students who do well in financial literacy are also likely to perform well in the PISA reading and mathematics assessment, and students who have weak financial literacy skills are likely to do poorly in the other core PISA subjects.
On average across the 10 participating OECD countries and economies, however, around 38% of the financial literacy score reflects factors unique to financial skills.
The gender gap in financial literacy was found to be much smaller than in reading or mathematics. Only in Italy do boys perform better than girls, while girls do better than boys in Australia, Lithuania, the Slovak Republic and Spain.
Economically and socially advantaged students scored much higher than less-advantaged ones.
When it comes to the performance of Irish teens in the PISA subjects of science, mathematics and reading, they ranked higher than the OECD average – though science and reading have dipped in more recent years...