The waste audit is the fourth session in the school outreach programme, and it is the one the students run themselves. Four bins, four days, a bathroom scale and the app.
Sixty-one percent of the school's weekly waste by weight turned out to be food and organic — most of it uneaten portions from a single supplier's packaged lunch.
The head teacher changed the portion sizes on the order the following term. No campaign, no poster — a number the children produced themselves.