A brilliant DT project (1 week of afternoons) where pupils design and make their own elastic band powered cars.
I've done this with pupils in Years 4, 5 and 6 and with my own children at home and they love it.
When I've done it in school we make sure to race the cars at the end of the project. The races can vary to ensure there are lots of winners e.g. fastest car, car that travels the furthest, best design, best team effort etc.
Hope you find it useful.