Crowded around a workshop table, four girls at de Zavala Middle School puzzled over a Lego machine they had built. As they flashed a purple card in front of a light sensor, nothing happened.
The teacher at the Dallas-area school had emphasized that in the building process, there is no such thing as mistakes. Only iterations. So the girls dug back into the box of blocks and pulled out an orange card. They held it over the sensor and the machine kicked into motion.
