Classroom teachers could earn as much as their deputy head by taking on paid overtime without extra management responsibilities.
The scheme, announced by Education Secretary David Blunkett last week, could see staff earning up to Pounds 5,541 a year extra by taking part in summer literacy schools or after-hours homework clubs. The calculation is based on 15 hours a week for a 38-week year, at an hourly rate of Pounds 9.72.
Unions representing heads and classroom teachers believe the scheme might damage the recruitment of senior staff.
Kerry George, senior assistant secretary of the National Association of Headteachers, said: "If a classroom teacher is able to earn the same amount as a primary deputy without having to take on the extra management responsibilities, why would anyone bother to seek promotion?
"School managements are increasingly under pressure with new duties to deliver the Government's standards agenda. If teachers opt to work extra hours to boost their pay, this will undermine the pay structure and make it even more difficult to attract staff to school management."
Teacher unions already fear that the creation of advanced skills teachers - to be paid in line with heads and deputies - will tempt teachers away from holding department headships or other management positions.
The Government aims to have homework clubs and other out-of-school activities in at least half of all secondaries and a quarter of primaries by 2001. Governing bodies will be able to pay full-time teachers who volunteer to take part in these activities outside the time they are contracted to work.
The pay review body's report said: "We welcome the major expansion of out-of-school learning support activity, staffed by teachers and other adults. The new programme will require many teachers to work additional hours in what might otherwise be their own free time. It therefore seems right and necessary there may be scope for extra payment."
The recommended sum is based on the additional duties allowance for teachers in residential schools. This would allow a teacher on point 9 of the pay scale to earn Pounds 28,058, which compares with Pounds 28,065 earned by the average primary deputy.
The pay review body said it would monitor the situation. Some fear teachers will do their marking while supervising pupils doing set homework.
But a spokeswoman for the Prince's Trust, which runs 500 homework clubs, said: "Teachers are very much involved in giving children one-to-one attention with coursework or helping them work their way through a computer program."
Pay award, page 8