Headteachers should come out of their cosy offices and show they can still hack it in front of a class, according to Britain's second largest teachers' union.
The NASUWT will propose at its conference next week that heads who do not teach regular timetabled lessons should demonstrate they meet the basic standards for qualified teachers.
The motion, put forward by the union's executive, says heads who have become divorced from the day-to-day reality of teaching do not understand the challenges of working in the classroom.
The motion will be supported by David Cornwall, head of St Matthew's Cof E primary in Westnewton, Cumbria, who teaches for 80 per cent of the timetable.
"Headteachers have the word 'teacher' in their title - they should not be school managers," he said. "If they are not teaching regularly themselves how can they understand the pressures, the tensions - even the joys - that their teachers experience?" he said.
Chris Keates, NASUWT general secretary, said out-of-touch heads were a minority but causing mounting casework for the union.
The union hopes the motion will influence the School Teachers' Review Body, which is examining the role and pay of school leaders.
Mick Brookes, general secretary of the National Association of Head Teachers, said: "We are more worried that heads are spending too much time in the classroom when they should be leading and managing schools."
Paul Kitson, head of John Spendluffe technology college in Lincolnshire, said not teaching meant he could concentrate on supporting staff. He said that he saw himself "more as coach than as a player".