When discussing different types of greenhouse structures, I have my students build a small model of each type (A-frame, uneven span, even span, connected) using spaghetti and marshmallows. Its cheap, not too messy and yummy! I would open the marshmallow bag early to allow them to harden up a bit, fresh marshmallows will tend to allow the structure to sag. I allow about 15-20 minutes for this activity.
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