Students made their own "sail" boats out of recycled materials for fun science . They used about 9 or so 40 minute periods and worked in small groups.
In my class, students had a lot of freedom and ownership of their boats. I gave them guidelines and materials. They could also bring in their own materials. I made sure their design would at least float. It was a great experience although a bit hectic at times managing a class full of second graders pretty much in free mode while building their boats. My two classes ended up winning 8 out of 11 prizes including fastest and most environmentally friendly (the same boat).
It's interesting that some teachers chose a different philosophy and made the boats for the students. Their boats were nicer than ours, of course, but I don't think their students had much fun or took ownership of the boats.
Some winners below. I love teaching.