I came across something called Goodhart’s Law today. It can be summed up as this: “When a measure becomes a target, it ceases to be a good measure.”

A few years ago I wrote two books about teaching, and one of the central planks of both books – alongside the joy and chaos of classroom teaching, and the Gordian knot that is relationships – was exactly that point. I put it slightly different to Goodhart, and my take goes like this: “Hitting targets is not difficult. It’s what you jettison in order to hit those targets that is the issue.”