One lesson that I have had a lot of sucess with is a 3-D big city project, done with 3rd or 4th graders. Here are the basics:
* Cut several pieces of old mat board (I use donated corner pieces from a frame shop) into 3.5 or 4" by 10" strips.
* Have each student choose 5 strips to design
* Each strip should be a different color
* Using a ruler or shapes to trace, change the shape of each strip to reflect an original architectural design.
* Draw several straight lines across the strips, using the ruler's width as a spacer.
* I use pre-made paper mosaics as windows on this project, but kids could make thier own by cutting strips into squares.
* Dry fit several windows to see how many it takes to get across the given building
* Place a dot of glue for each square on building and begin gluing, using the lines as guides to make rows and columns of windows.
* When all buildings are complete, assemble them as a sculpture, using a strip of mat board as a backing board. Use chunks of scrap fomecore to raise each building to a different level on the backing board, and overlap each building slightly to create a relief sculpture.
* Use hot glue for this, it works well with each material.