Pupils are losing out in the classroom because older teachers are being forced out of their jobs by school management, a teachers' union has warned.

At an educational conference in Birmingham on Sunday, the NASUWT union claimed that school children would suffer as a result of older, more experienced teachers being pushed out before they reached their pension age.

According to the union, women teachers are most at risk of feeling under-valued and pressurised into quitting their posts before retirement.

Chris Keates, NASUWT's general secretary, said that low starting salaries and slow pay progression had also contributed to one of the worse teacher shortages since the Second World War.

"A key contributory factor to the crisis is the competitiveness of teachers' pay and rewards compared with pay of graduates in other occupations," she said.

"The Westminster Government's pay restraint in England and Wales has been compounded by schools setting increasingly higher barriers to pay progression."

Ms Keates added: "The Government now expects people to work longer, but the irony in teaching is that those with the experience and expertise are in too many cases being hounded out of the profession because they are older and more expensive.

"Older teachers are disproportionately facing being placed on capability procedures, report being denied access to professional development and are often put under intense pressure to leave their job.

"The losers of course are not just the teachers themselves, who often are forced out of a career they love, but the pupils, who are losing experienced, specialist teachers.

"The lack of action by the Government to promote respect and dignity for working people has led to a culture of disrespect and discrimination in schools."

The union has called on the Government to change the culture in schools to ensure that ageing teachers are valued - and not penalised - for their experience and expertise.

It argued that new strategies should be implemented to tackle age discrimination in the classroom, in order to warden off the growing threat of capability assessments and job losses.

Ms Keates also threatened industrial action if schools continued to "worsen" pay and conditions for teachers.

A Department for Education spokesman said: "Older teachers bring a wealth of experience and expertise to the classroom, and their contribution should be valued.

"Any form of discrimination, including age discrimination, is completely unacceptable.

"We set up the Working Longer Review, and we are working closely with NASUWT and others to cover the issues related to teachers retiring later."