Tens of thousands of teachers approaching retirement want to reduce their responsibilities and hours, but half of schools are opposed to offering them part-time work, government research shows.
A study reveals a huge shift in teacher career patterns, with two-fifths of the 4,000 49 to 60-year-olds interviewed considering using new pension flexibilities to gradually wind down their jobs.
Many will work until they are older than previous generations, mainly because they need the money and, to a lesser extent, because they enjoy the job.
Heads told London Metropolitan University and BMRB, a market research agency, that they were interested in the contribution older teachers could make in mentoring less experienced colleagues, covering lessons and working with small groups of pupils. But they were seen as a costly compared to newly-qualified teachers and support staff.
Heads also feared that shorter hours would create timetable problems and reduce continuity for pupils, with 56 per cent of secondary and 49 per cent of primary heads saying they would be unhappy employing more part-timers.
The study was commissioned by ministers to measure the impact of changes made to the Teachers' Pension Scheme in January 2007 to allow more flexible retirements.
Teachers who have started work since then will have to work until they are 65 instead of 60 before they can claim a full pension. But the study suggests the average retirement age will rise long before the increased pension age takes effect. The past two decades have consistently seen more than half of teachers retire before the age of 60, but only a quarter of the current crop of over-49s plan the same.
Half of all heads interviewed saw meeting the needs of older teachers - over-50s now make up 30 per cent of the workforce - as part of providing quality education. But half of the secondary heads saw older teachers' interests as incompatible with those of their schools.
Interviews revealed teachers who thought they were knowledgeable on pensions often got facts wrong.
Almost all teachers who thought they knew how much they would lose from their pensions by retiring early had underestimated the cost. The study found the new "phased retirement" flexibility, which allows teachers to collect some of their pension while continuing to work, requires them to reduce their salary by a quarter.
The study recommended making the salary reduction 20 per cent, to allow teachers in phased retirement to work four-day weeks.