the weird thing about kids and maths is how some find arithmetic puzzles intuitive but can't cope with transferring that onto paper.

At 6, my not-academic son could answer questions like: It takes 50 bricks to make a one square metre wall. How many bricks are needed for a wall 6 meters long and two meters high?

At 15, he absolutely struggled with even simple GCSE math. Very very painful long sessions of tutoring him and he managed a bare C.

He's 23 now and has an intuitive grasp of ratios, fractions, equations and the real world problems that can be tackled (fish is supplied in whole kilograms. Servings are in x hundred grams. Chef wastage is x percentage of servings. 48 hour shelf life and y dishes sold per day, what is the most efficient quantity of fish to buy?). It's quite impressive.

But present him with abstract symbols and he goes blank.