I like this idea a lot because it'll show them the value of thinking about the design and coming up with something that can be adapted and modified as new requi

I like this idea a lot because it'll show them the value of thinking about the design and coming up with something that can be adapted and modified as new requirements come in. If you just do a series of unrelated challenges, then there won't be an incentive to come up with a good design that can last.