Regression to the mean

Hanging with engineers is fun, but one cannot presume that it doesn't rub off. For instance, Carroll told me the following story:

Kenny, my 10-year-old son was talking to our dental hygienist who remarked that since both his parents had Ph.D's he would probably be pretty smart himself. Kenny replied that he probably would unless regression to the mean kicked in. He then had to explain what regression to the mean was.