Higher staff pay may mean larger classes, says Ofsted
Head teachers may have to increase class sizes if they are to pay the best teachers higher wages, the chief inspector of schools in England admits.
Sir Michael Wilshaw said schools could not afford "highly paid" staff while keeping class sizes small.
A new system of performance-related pay is being introduced for teachers in England from September this year.
The move has met with resistance from teachers, but the government says it is vital to recruit and reward the best.
Speaking at a seminar organised by the think-tank, Reform, Sir Michael, former head of Mossbourne Academy in Hackney, London, said: "The good heads know they have got these additional freedoms and will reorganise.
"[As] an ex-head teacher, I always said to the staff, 'I want a highly-paid staff, I want to reward those of you who are prepared to commit yourself to the school and do a good job in the classroom.
"To do that, might mean that we have larger classes. You can't have both. You can't have small classes - small groups - and a highly-paid staff.
"It might mean that head teachers have got to make [that choice]… So negotiation with the staff is going to be important."
On the issue of performance-related pay for teachers, Christine Blower, general secretary of the National Union of Teachers, said: "This is an invidious choice no head teacher or governor would want to make.
"It gives the lie to the idea that changes to teachers' pay are a free chance for heads and governors to pay 'good teachers' more. The simple fact is there is no more money in the pot."
A spokeswoman for the Department for Education said: "It is vital that schools can recruit and reward the best teachers.
"We are reforming pay so schools can attract and retain the best teachers who have the greatest impact on their pupils' achievements.
"We expect heads to be able to judge what is best for their pupils."
Teachers' pay rises have previously reflected their length of service, but under the new reforms, there will be a stronger link between achievement and pay progression.
Advice to head teachers from the Department for Education suggests teachers' performance might be measured on their impact on pupil progress and on wider outcomes for pupils, improvements in specific areas, such as behaviour management or lesson planning, their impact on the effectiveness of other staff, as well as their wider contribution to the school.