It was the first day of Grade Three in a new town for Johnny. As a
test, his teacher went around the room andasked each of the students
to count to 50.  Some did very well, counting as high as 30
or 40 with just a few  mistakes.  Others couldn't get past 20.  
Johnny, however, did extremely well; he
counted past 50, right up to 100 without any mistakes.  He was so
excited that he ran home and told his Dad how well he had done. His Dad
nodded and told him, "That's because you are from Iowa, son."

The next day, in language class, the teacher asked the students to
recite the alphabet. It's Grade Three, so most could make it half way
through without much trouble. Some made it to S or T, but Johnny
rattled off the alphabet perfectly right to the end.  That evening, 
Johnny once again bragged to his Dad about his prowess in his new
school.  His Dad, knowingly, explained to him, "That's because you are 
from Iowa, son."

The next day, after Physical Education, the boys were taking showers.
Johnny noted that, compared to the other boys in his grade, he seemed
overly "well endowed".  This confused him.  That night he told his dad,
"Dad, they all have little tiny ones, but mine is ten times bigger than
theirs.  Is that because I'm from Iowa?" he asked.

"No, son," explained his Dad,
"That's because you're 18."