Pat Kyrou, a teacher from Essex and a member of the Association of Teachers and Lecturers, raised the issue during a motion at the Trades Union Congress Women’s Conference in London.
She told delegates that “an unexpectedly large number” of teachers who are put on capability are female and over 50.
She said: “Until older women have a similarly respected profile to that of older men, their abilities will be under-appreciated and they will be more likely to experience discrimination in all aspects of the job market.”
Ms Kyrou pointed to figures that showed the average salary for female teachers in state schools in 2012 was £36,600, while for men it was £39,900. She also said that fewer women are promoted to senior roles in schools.
In moving her motion, Ms Kyrou raised fears that the new links between performance management, pay and capability would become “a terrifying stick with which to beat education staff”.
She added: “Schools can use performance management as an opportunity to get rid of anyone too old, too expensive, or whose face doesn’t fit, by setting effectively unachievable targets.
“We are noticing a trend that education staff will resign rather than be dragged through formal disciplinary procedures, with the result that sometimes it can be as little as three weeks between the first communication from management and the end of a decades-long career in education.”
The motion, which was passed, called for the TUC and its member unions to work with organisations such as The Age and Employment Network to support older workers in the workplace, to raise awareness of the effects of discrimination, and to promote the benefits of flexible working more widely.