"They're so bright, they should know better"

Some readers will feel that the capacity argument doesn't apply to their child. Sam reads two years above his age. He beat you at chess. A child who can do that can remember a kit, and the fact that he doesn't is more damning, not less.

Diamond's review addresses this directly, as one of the controversies in the field. The relation between the executive functions and what psychologists call fluid intelligence, the ability to reason and solve new problems, is contested, and the contest exists because they don't line up neatly. Children can score highly on tests of reasoning and be at the age norm, or below it, on tests of inhibition or working memory, and the reverse. Being able to see the solution to a chess problem is a different thing from being able to stop a game when asked, and the second doesn't follow from the first.

This is one of the commonest patterns parents describe, in my experience, and one of the most puzzling to them. The bright child who forgets everything. The child who can explain how the tides work and can't find their shoes. The puzzle dissolves when you separate intelligence from organisation. They're different equipment, on different timetables, and a nine-year-old can be far along on one and exactly where you'd expect on the other. Brightness doesn't pull the executive functions along with it. If anything, a bright child spends more of their attention inside their head, where the interesting things are, and less on the hall floor, where the coat is.

"They should know better" also confuses knowing with doing. Sam knows the kit should be in the bag. Ask him and he'll tell you. Knowing is a fact in his head. Doing it alone at twenty to nine is inhibition, working memory and time judgement working together under pressure, and chapters 3 to 6 are about why those are still growing. The brighter the child, the wider this gap can feel, because the knowing is so evidently there and the doing so evidently isn't, and the parent concludes that the only thing missing is will.

What's missing is age. The chess will still be there at fourteen. So will the kit, in the bag, if the handover has happened.