We also built cubes using marshmallows and toothpicks. As we were building, some of our cubes were tilting to one side. We talked about how we could build a stable structure and how we needed to ensure that the joints (or corners as they were also called) were secure and strong. During the second STEM class, we finished up our cubes, in case they were not quite complete, and then tested their strength by placing a light book on them.