All of the boys in the class predicted that the Legos stuck together would weigh more/have more mass than the same Legos, loose. In illustrations, they provided their reasoning.
They then got to work testing their predictions. In pairs, they first weighed the attached group of Legos, and then took the Legos apart, weighing them in loose pieces. This led to a most unexpected discovery and squeals of surprise for the groups that were careful with their measuring: the Legos weighed the same!
Exactly. And how powerful that the boys came to realize this not by being told, but through their own experimentation. This is how the testing of ideas drives true learning.