Teachers' pay falls significantly behind that of other graduates the longer they stay in the profession, research commissioned by the NUT has found.
Salaries start lower and fail to increase at the same rate as other graduate jobs in both the private and public sectors, the independent study concluded.
After five years' experience, teachers outside London currently earn Pounds 30,148. But if their salaries had increased at the same rate as those of other graduate professions, it would be 7 per cent higher at more than Pounds 32,200.
The gulf is even bigger after 10 years. A teacher outside London at the top of the upper pay scale is now earning just over Pounds 35,100 a year.
If the profession had kept pace with other graduate jobs, they would be receiving 13 per cent more money at over Pounds 39,600, according to the research.
The study was commissioned by the NUT in support of its claim for an above-inflation pay rise this year.
The union has submitted evidence to the School Teachers' Review Body, which recommends pay increases to the Government, calling for a 10 per cent rise for teachers or an extra Pounds 3,000, whichever is highest, from September.
It is also lobbying for a one-off bonus to make up for below-inflation pay deals since 2005. Teachers' salaries have suffered a 6 per cent drop in real terms in the past four years, the union said.
The new research, conducted by Income Data Services, builds on previous work that compared starting salaries for teaching and other graduate jobs.
As well as progressing more slowly, starting pay for teachers is behind average salaries on offer in other graduate professions.
The average graduate job pays more than Pounds 35,300 after five years and more than Pounds 41,800 after 10, according to the research.
Law and accountancy had the best starting salaries, with an average of almost Pounds 29,700.
Teachers' pay also performed poorly compared with salaries for health professionals, including doctors, psychologists and pharmacists.
Salaries for health professionals are 16 per cent above those for teachers in their twenties. But by the time they reach their forties, secondary school teachers are earning 24 per cent less and primary teachers 36 per cent less.
Christine Blower, NUT acting general secretary, has warned the Government not to use the recession as an "excuse" to offer a low pay deal.
Unless pay is improved, graduates will be drawn to other jobs that pay more and are less stressful, Ms Blower said.
"Giving teachers a fair wage for the job they do is something from which the STRB and the Government must not shy away," she said.
The NUT and the other teaching unions are all lobbying for a pay rise of more than 2.3 per cent, a figure first suggested by the STRB in a report last year.
They argue that the recession will only have a temporary impact on teacher recruitment and that pay needs to be improved to attract the best graduates.
A spokesman for the Department for Children, Schools and Families said that average teachers' pay has increased by 19 per cent in real terms since 1997, with classroom teachers now earning Pounds 31,400.
A decision on pay from this September is expected later in the year.