May shows poor grasp of data in grammar debate

Janet Downs's picture
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If you look at the attainment within grammar schools, poorer children do better in grammar schools than they do in other schools, in the sense that the attainment gap between poorer children and better off children is virtually zero in a grammar school, so the education is really helping those children.

Prime Minister Theresa May, reported in Independent

But May makes an elementary statistical mistake: ignoring sample size.  Let’s take one of the largest selective counties, Lincolnshire.  Three of Lincolnshire’s fourteen grammars had so few disadvantaged* pupils in the 2015 GCSE cohort that results were suppressed.  Caistor Grammar School, for example, had just one disadvantaged pupil out of 95. 

How did those with a higher proportion of disadvantaged pupils fare?   At Queen Elizabeth’s Grammar, Alford, eleven of 92 pupils (12%) were disadvantaged.  100% reached the benchmark (5 GCSEs A*-C including Maths and English) against 94% of advantaged pupils.  Similarly, the seven disadvantaged pupils at Bourne Grammar outperformed 142 advantaged pupils by four percentage points.

But this wasn’t the case elsewhere.   At Queen Elizabeth’s Grammar, Horncastle, the 107 advantaged pupils outperformed the eight disadvantaged pupils by eight percentage points.   At Kesteven and Grantham Girls’ School, 172 advantaged pupils outperformed eight disadvantaged pupils by nine percentage points.  At Skegness Grammar, where nine of 93 pupils were disadvantaged, the gap was wider: 16%.   So much for May's generalisation that the gap between advantaged and disadvantaged pupils in grammars is 'virtually zero'. The small sample sizes make it impossible to come to reliable conclusions.

May would still argue, however, that poor pupils in grammars perform better than elsewhere.  That’s true, but the poorer pupils elsewhere comprise the whole ability range while grammars choose only high ability poorer pupils.  It’s hardly surprising that pupils selected for their high ability, whether poor or not, perform better than all pupils elsewhere.  It’s worrying that a PM with a BA from Oxford hasn’t grasped that obvious point.

If May is correct that grammars improve performance for disadvantaged pupils, then Lincolnshire’s selective system should raise the performance of all such pupils.  But it doesn’t.  In 2015, 30.10% of the county’s disadvantaged pupils reached the benchmark: 6.6 percentage points lower than the national average for such pupils of 36.70%.  The same is true in Kent, another large selective county, where the proportion of disadvantaged pupils reaching the benchmark in 2015 was 30.5%.

May claims new grammars wouldn’t be a return to the old binary system.  But it would.  Where grammars exist, now or in the future, there’s a perception that there are top schools for top pupils and a lower group of schools catering for the rest.  Grammars may be relabelled ‘centres of excellence’ but this won’t hide the fact that non-grammars will be perceived as centres of not-quite excellence for the majority of children, poor or not, who aren’t labelled ‘top’.

This is no way to set up a school system that works for everyone.  It doesn’t and it won't.

This is a companion piece to Eleven grammar school myths, and the actual facts which has been read nearly 15,000 times since the site was updated earlier this year.

 

 *Department for Education school performance tables define disadvantaged pupils as ‘those who were eligible for free school meals at any time during the last 6 years and children "looked after" (in the care of the local authority for a day or more or who have been adopted from care)’.

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