Recently Your Friend Martha Took Her Sons to a Hands-On

Recently your friend Martha took her sons to a hands-on children's museum. Martha noticed that her 8-year-old son and her 12-year-old son interacted with some of the displays in very different ways. One display involved opening doors to safes by determining the correct combination. Each safe had three, four, or five buttons that had to be pressed in a particular order to open the door. Martha's 8-year-old son randomly pushed the buttons and never found the correct combinations to any of the safes. Martha's 12-year-old son approached the task in a very systematic manner - trying all possible combinations of buttons until the doors opened. Now Martha is concerned that there is something wrong with her younger son. What can you tell Martha about the differences in concrete operational and formal operational thought that might explain her sons' behavior?