These stay there for a week. At the beginning of each day, every child has to decide what two items they are going to buy. They have a certain amount of spend, say pound;100. Every day the prices change - one day it'll be cheap trainers, and the next, more fashionable, expensive ones. The idea is to get as much as possible for your money and to work out the sums correctly. We give them accounting paper to do their calculations.
When I do this with lower-ability children, I tend to use smaller sums of money and simpler prices - for example, pound;3 rather than pound;3.99. I give prizes for the one with the most money left over and the one who has worked it out best. The children really get into it and there are howls of delight when they realise they've got a bargain. And they've grasped subtraction by the end of it.
Daisy Harman, class teacher, Ravenstone Primary School, London borough of Wandsworth