Wednesday, June 14, 2017 at 11:00am. Tweens (completed grades 4-8) in 20 minutes, build the tallest, free-standing structure out of 20 sticks of spaghetti, 3 feet of tape, 3 feet of string, and one large marshmallow. The marshmallow must be on top. Grab some teammates and see if you can crush the competition in creating the tallest “marshmallow on top structure”. We’ll celebrate the challenge with decorating Rice Krispie treats!