Hi Peter,
Good idea BUT please don't just do a tying 100 knots or the longest chain of knots etc, do something with a purpose and a tangible end result to make the project worthwhile. Something like pyramid teaching - one scout teaches two people, those two each teach two more and so on, the names being recorded back down the chain. Maybe you could have a Reef Knot pyramid, a Bowline pyramid and so on. Just an idea to get the grey matter thinking.
Keep us informed
Gordon