The structure our club takes on is that one day students will brainstorm, plan, design, and begin construction and the second day they will build and share. Piggybacking off the Curiosity landing of the third Mars Rover, students made a moving rover. They must decide if they will go with the prototype provided, or branch out into something new. You can find the plans through the picture link below.
During the next meeting, students will be asked to construct a pedistal to hold a "priceless" sculpture using only sentence strips (no need for those in junior high) and 1 meter of tape. This was an activity I did the first Saturday class I took for the Engineering for gifted students class. (I love my district for providing such great PD!!) These are the examples that we came up with...
This was our design. Probably could have done just as well without the sides cut.
The strongest tower. Each square had additional reinforcement inside.