Hi...liking the sound of this project! Were you just going to make the crowns out of card? If you wanted to increase the difficulty level you could try making them out of straws, or basket weaving (?!) wire and mod-roc maybe too dangerous for younger hands. Craft foam is fab also, the stuff you heat to mould it to the shapes you want...that gets science i there too The research and design process could be made as advanced as you like however, and if you give the students shiny plastic gems and glitter, and discuss the gory parts of Henry VIII's love of beheadings they are sure to be engaged and learn. If I think of anything else Ill let you know.