The case in three lines. The Green Gazette's front page says Saturday jobs pay £48 a week on average, from the paper's own survey of twenty-five students. A bookshop owner and a Year 9 washer-up write in, because neither is anywhere near £48. Written in order, the middle reply is £20, twenty-three of the twenty-five are below the average, and Tara has to write the corrections box.

One question to ask. "What should the box say?" Then: "Should the two biggest replies be taken out?" Let them argue both sides.

One thing to do at the table. Ask everyone at the table how many minutes they spent on a phone or a screen yesterday. Write the numbers down smallest first. Find the middle one, then work out the average. Say both out loud, and see which one the biggest number pulled.

The grown-up layer. The case separates the mean (the total shared out) from the median (the middle value), and a clarification from a retraction. It gives the reporter her strongest point, that removing awkward replies would be cooking the numbers, and gives the shop owner his: a true number can still do harm. The habits it models are going to the original sheet, writing every value down in order, and giving the typical case its number without erasing the unusual one.

The case leaves the line blank on purpose. Ask for it before you offer yours.