I've recently started doing an in depth maths investigation each week with my Y4 class. The idea is to get them used to taking a structured, logical and organised approach to solving an extended problem, in an interesting context eg Whodunnit? type investigations, rather than 'send so and so on holiday with such and such of a budget' which has become a bit drab by now. I've found and completed 3 really lovely ones - saving the world from an alien virus, a mystery party venue and a Whodunnit? - and now I'm floundering to find more! There are word problems galore, but I'm hunting for open ended investigations that will take a Y4 two sessions to explore, understand and solve. There seems to be plenty for UKS2 and KS3, but that would obviously be too challenging. Can anyone suggest anything?