We finished our Pushes and Pulls science unit this week with a design challenge.   We began the unit by reading a story about Milo, a girl who wanted to put a swing set in her back yard.  The area that she hoped to use had many large rocks that needed to be moved.  Students were asked to create a model that would use pushes and/or pulls to move the rocks over a distance (we decided at least 3 feet).  They did a wonderful job of thoughtfully tackling this problem, trying out multiple ideas, and adjusting their models when needed.  We saw lots of clever ideas from various containers that could be used to pull the rocks to a "zip line," which needed something heavy at either end to keep it anchored.  It turns out classmates work quite well for this job!  We spent time talking about changes children might make to their designs if they were presented with the same challenge again, and the idea that engineers are constantly revisiting things they design, always trying to find ways to improve their creations.