My son is 5. He just started kindergarten, but has been asking challenging questions since he was able to talk. On the way to school one day he asked what “Percent” means. That’s a pretty profound concept for a little guy to wrap his head around. As I tried to find a metaphor or something to compare it to, I realized what I needed was a mental model that fit in the world of a 5 yr old.

Last year we took our first family vacation. I loved watching my son’s reaction to the icons and symbols he saw on our travels. He regularly called out pictures such as no smoking signs, train, bus and restaurant icons. It occurred to me that children are a great litmus test for the effectiveness of visual information displayed to a general audience or in situations where written language is ineffective.

Moments like these are great mental design exercises. Nearly every project requires me to create a virtual environment that makes sense to users whose frames of reference are very different from mine. Sometimes I am guilty of forgetting that what makes sense to me doesn’t matter. The design needs to fit into the world of those people who will use it.

As for explaining the concept of percentages, I thought of the 4 out of 5 dentists recommend tagline. I told him that it’s a way of pointing out how many out of a group are different in a certain way from the rest. “For example, if there are 10 kids in your class, 2 are wearing yellow shirts and the rest are wearing red shirts, you could say that 20 percent of your class are wearing yellow shirts.” That seemed to makes sense to him. Now if I could just come up with a good answer for his question today, “Mama, why is there war?”