Two out of every five teenagers in Northern Ireland leave school without the basic reading and writing skills, it has been revealed.
An audit office report into literacy and numeracy levels said unacceptably large numbers of pupils were not making the grade.
Kieran Donnelly, Comptroller and Auditor General said more must be done to tackle the growing problem of educational underachievement.
He said: "Regardless of how well the majority of pupils perform, it is also clear from our findings that unacceptably large numbers of pupils are failing to achieve even minimal levels in literacy and numeracy.
"It is vital that our education system does all it can to address underachievement in order to improve the life chances of our young people and to ensure that our economy is well equipped to compete in an increasingly global market place."
Audit Office officials visited 10 primary and 10 post-primary schools as part of their examination during the 2010/11 term. They found that, as students progressed through the system, the numbers reaching the expected standard in maths and English declined.
At the end of primary school more than one in six students (3,876) did not meet the required minimum standards. By aged 14 (key stage 3) that had slipped to one in five.
By GCSE level, aged 16, two out of five pupils (9,000) failed to achieve the standards deemed necessary to progress to sixth-form studies, further education or step on to the employment ladder.
The report found a correlation between educational under attainment and low family income. By the age of three, poor children were one year behind richer students in terms of communication and in some disadvantaged areas up to 50% of children started school without the essential skills.
Pupils entitled to free school meals had a substantially lower pass rate than those not entitled and were only half as likely to achieve five GCSE grades A* to C.