"What caught the attention of Michele Belot and Jonathan James, though, was the way Oliver's project had been implemented. Belot and James – economists at Nuffield College, Oxford, and at the University of Essex respectively – noted that the campaign had created a near-perfect experiment. The chef had convinced Greenwich's council and schools to change menus to fit his scheme; he mobilised resources, provided equipment and trained dinner ladies. Other London boroughs with similar demographics received none of these advantages – and indeed, because the programme wasn't broadcast until after the project was well under way, probably knew little about it. The result was a credible pilot project. It wasn't quite up to the gold standard of a randomised trial, but it wasn't far off.
Thanks to the UK's exhaustive school testing regime, Belot and James were able to track pupils' performance in some detail. They concentrated on primary schools, figuring that secondary school pupils could (and probably would) avoid eating school lunches that were too worthy. (This is surely correct. My own habitual sixth-form lunch was four bars of chocolate – a pound a day well spent.)
Their answer – a provisional one, since they are still refining the research – is that feeding primary school kids less fat, sugar and salt, and more fruit and vegetables, has a surprisingly large effect. Authorised absences, the best available proxy for illness, fell by 15 per cent in Greenwich, relative to schools in similar London boroughs. And relative to other boroughs, the proportion of children reaching Level Four in English rose by four and a half percentage points (more than six per cent), while the proportion of children achieving Level Five in Science rose by six points, or almost 20 per cent. There is some uncertainty about these numbers: they could be substantially smaller or larger. There is not much that can be said with confidence about scores in other subjects, or other achievement levels – although the academic benefits of the Greenwich lunches appear to be positive, if tentatively so, in almost every case."
Politicians should talk about the cost of things as a % of GDP, not in millions and billions.