The Association of School and College Leaders and the National Association of Head Teachers say teachers will only be prepared to take on headship if the financial incentives are great enough.

They made a joint submission to the School Teacher Review Body this week, calling for the “statutory differential” between top classroom teachers and assistant or deputy heads to be widened.

Headteachers should also earn significantly more than deputies, to encourage them to move upwards, they advise.

They have also called for compensation packages to be built into contracts of teachers taking on “high risk” apppointments in difficult schools.

Due to workforce remodelling, and the introduction of financial incentives to keep good teachers in the classroom, the teacher on the lowest level of the leadership spine can get less than the top classroom teacher.

Kerry George, senior assistant secretary for salaries at the NAHT said: “If a teacher is on point three of the upper pay scale, with a teaching and learning responsibility payment, they will be earning pound;35,750. The lowest rank on the leadership scale is pound;34,083.

“In a small primary, a headteacher can earn as little as pound;38,500, which can mean their staff can earn comparable rates without the extra responsibility.”

The unions have proposed that extra pay flexibility is given for heads taking on extra responsibility in the form of children’s centres and extended schools. They say heads are currently having to accept pay arrangements of “inadequate or questionable legality” to be rewarded for the extra work.

The unions are also concerned about the increasing vulnerability of heads.

Last year, 28 ASCL members reported that they were made to resign or sacked and the union is dealing with 22 heads and 19 deputies and assistants whose jobs are under threat.

The unions want the review body to recommend that employers include an “exit package” with clear levels of compensation in the event of a contract being terminated. This, they say, will make posts in tough schools less of a high risk career move and will allow them to attract the good quality heads they desperately need.

Mick Brookes, general secretary of the NAHT said: “A built-in compensation package of one year’s salary would not be out of order for a head prepared to take on a school with a record of difficulties in raising standards.

“Because of short-term targeting, heads are given months to turn schools around and if they don’t, they are regarded as failures. You would hope they would never have to receive the compensation but it might just mean more heads are prepared to take the risk.”