Yesterday, Schools Week reported on analysis by Education Datalab which showed almost 1,200 schools would be defined as “coasting”, as a definition for the term was finally put forward by education secretary Nicky Morgan. Henry Stewart, co-founder of Local Schools Network, believes that figure would be more than double. Here he puts forward his case.

On Monday night education data geeks worked late into the night to try and work out how many schools would be categorised as coasting under Nicky Morgan’s new definition. The Education Datalab came up with a figure of 1,179 schools, while my analysis resulted in an estimate of 2,833.

The Department for Education (DfE) stated “those secondary schools that fail to ensure 60 per cent of pupils achieve five good GCSE grades and have a below average proportion of pupils making expected progress over three years, will be classed as coasting”.

The Datalab figure is based on schools being below 60 per cent in each of three successive years and below the average for expected progress in both Maths and English for each of the last three years. My calculation was based on being below 60 per cent for two years, and below average expected progress across the three years, rather than in each of the three years.

What both of us are agreed on is that the measures that have been chosen will, especially for secondary schools, target schools with low attainment at entry and those with high numbers of disadvantaged students. Datalab’s secondary graph is a powerful demonstration of that.

On my calculations, for secondary schools where fewer than 20 per cent of students are classed as disadvantaged, only 8 per cent are set to be termed coasting. The figure for those with more than 20 per cent disadvantaged is four times as much at 39 per cent.

The secretary of state, in announcing the definition, stated that “for too long a group of coasting schools, many in leafy areas with more advantages than schools in disadvantaged communities, have fallen beneath the radar”.

However, if this was genuinely Morgan’s intention, she has chosen the wrong measures. This is far from the truth. For example, no grammar school will be classed as coasting because all – with their high attaining intake – easily manage to get 60 per cent of their students to 5 A-Cs.

The first secondary measure, the proportion achieving 5 A-Cs including English and Maths, is closely related to the intake at age 11. Some schools, with low attainment, score a strong value added while only getting 55 per cent to the GCSE benchmark. For those with a strong intake a result of 65 per cent may actually be “coasting”.

The second measure, the proportion achieving the DfE’s definition of expected progress, is also closely related to initial attainment. It defines “expected progress” as 3 levels whatever the starting point. But the data suggests far fewer students get from a level 3 to a D (3 levels) than from a level 5 to a B (also 3 levels). Indeed a school that gets 100 per cent of its level 5 students to a B, but only to a B, could accurately be described as “coasting” but would not be picked up under this definition.

Nicky Morgan is right to want to ensure all schools are enabling their students to reach their full potential. But she is wrong in both her definition of coasting and in the solution of forcing them to become academies.

Analysis of Ofsted reports shows that a school rated as inadequate is twice as likely to remain inadequate if it is a sponsored academy, rather than a maintained school. A sponsored academy that is rated good is almost four times as likely to fall to inadequate as a similarly rated maintained school.

Stand-alone converter academies seem to do fine. But the evidence increasingly suggests that converting a school to be a sponsored academy could slow its progress. The problem appears to lie with the multi-academy trusts that are involved. According to the DfE’s own analysis, of the 20 largest MATs, only four achieved value added in their students that was above average.

The centralisation that the academy programme has produced does not help to deal with coasting schools. A good local authority knows far better than the distant secretary of state, or the new Regional Schools Comissioners, which schools should – given their intake and local circumstances – be doing better.

I know of two directors of childrens services that have contacted the DfE to raise concerns about academies in their area that they feel should be getting better results. In both cases the response was that, as the schools were above the DfE’s floor targets, they were not a priority. And, if they are above the new definition of coasting, they will still not be a priority.

There are schools, often highly regarded by local parents, that should – given their intake – be achieving better results. However the best answer to this would be for local authorities to be able to bring their local expertise to bear and play a role, even with academies. For example, a right for local authorities to call in Ofsted would be a powerful negotiating tool. The new powers for the secretary of state will not provide the solution because the measures she has chosen will not affect the coasting leafy suburb schools that she claims to be targetting.