Teaching as a profession may be in long-term decline worldwide, according to the Organisation for Economic Co-operation and Development.
In its draft report, it suggests that policy changes, including targeted pay rises, will be required to increase the appeal of teaching.
The report says that as societies became richer and better qualified, job opportunities expanded, and teaching as a path to upward social mobility and job security became less attractive.
Concerns about the difficulties faced by schools, often fuelled by negative media reporting, have also damaged the profession.
Demands on schools have risen, while in many countries, resources have not kept pace.
Nevertheless, it says, policy initiatives can make a difference - as they have in France and Australia. In some countries, such as Korea and Ireland, teachers' social standing is high and there are more applicants than vacancies.
A total of 25 countries were studied for the report which sets out the challenges to recruiting, developing and retaining effective teachers. It says that in the majority of countries average salaries in the community have increased faster than teachers' salaries.
The large size of the teaching workforce means that to lift salaries across-the-board by even a few percentage points is very costly. It may be more cost-effective to target larger salary rises at the key groups in short supply.
Around half of the participating countries face teacher shortages, either at present or in the near future, as large numbers of teachers reach retirement age.
On average, 25 per cent of primary and 30 per cent of secondary teachers are over 50, and in some countries more than 40 per cent are in this age category.
A key part of any general strategy must involve reminding teachers that they are highly skilled professionals doing important work as teachers'
self-image is often relatively low.