One class, the 4th (age 9/10) designed the Nativity scene and made a draft in a big wallpaper to explain to the other classes the project.
They decided the characters and the main parts of the scene: the river with the lake, the village, the forest...
The 4th class was divided in several little groups, each one got a character or a scene to create: the river, the woodcutter, Maria, the Christmas tree and so on.
They got some help from the 5th class but just at the end.
While the other classes of the school were involved by a call to create some part of the scene like the forest, the village, the sky...
When each part was ready we helped the kids to assemble the whole in two tables.