Nicky Morgan's new definition of "coasting" represents two key elements:
a) a big expansion of the numbers of schools being targetted (see here
for my estimate of almost 3,000 schools)
b) a focus, because of the measures used, on schools with lower ability entries.
When Morgan first started talking of coasting schools, I assumed a key target would be schools with strong entries that do not add sufficient value in terms of exam results achieved. Such schools will in fact be almost totally unaffected by Morgan's new definition.
First, any school where 60% of students achieve 5 A-Cs will not be "coasting"
There are many schools with strong intakes for whom scores in the 60s are below what could be expected. Indeed for students arriving with a Level 5, the target of getting a C is the wrong measure in any case.
And there are 18 schools which have a Best8 value added score of over 1020 (ie, in the top 15% in the country) but still meet Morgan's new definition. This is not because the school is under achieving. Given their intake, the Best8 figure makes clear that they are achieving very well indeed.
Secondly, the "Expected Progress" measure is also linked to initial ability
Expected progress sounds like a value added measure. However "expected progress" is defined as 3 levels of progress, whatever level the students starts at. So for a student leaving primary school with a Level 5 grade, 3 levels of progress only means getting a B at GCSE. For a level 4 student it means a C, and for a level 3 student it means a D.
In Maths of those arriving with a level 5a, 96% achieve 3 levels of progress. However for those arriving with a 4c, just 48% get 3 levels of progress and, for those with a 3c, just 20% achieve 3 levels. How likely a student is to achieve "expected progress" is therefore highly dependent on their starting point. For a school, the % that achieves 3 levels of progress is likely to be very dependent on the ability of the intake at age 11. (Figures taken from 2014 Raise Online)
Imagine a grammar school where every student arrives with a level 5 grade. If they got only 65% to achieve 5 A-Cs at GCSE, achieved no A grades in English or Maths and got only 75% to even a level B then it would be fairly clear that the school was not doing well. However it would not trigger the coasting definition.
While I don't think any grammar school is doing that badly, it is fairly certain that no grammar school will be described as coasting under this definition. However secondary moderns (or comprehensive schools in selective areas) will have to be doing very well indeed to escape being termed coasting.
An odd choice of measures
From 2016 the new Progress8 measure will be used to define coasting. This is a genuine value added measure (though some have pointed out its weaknesses), that should be designed to reflect the progress of all students in a school.
A perfectly good value added measure exists, in Best8, and is available to the DfE. It is very odd then that Nicky Morgan has chosen instead to use a set of measures that targets the "coasting" term much more at those schools with lower ability entries.
Note: The graph has been added since the original post, and slight corrections to figures to fit those published in Raise Online.