In junior high we read a story about a farm boy who was required to
memorize a speech to be given at a school function. The boy memorized
the piece while milking and proved unable to recite it anytime else. 
The solution was to provide him with a rope belt knotted behind his
back, the ends of which he could pull like udders.  Unfortunately, a
mirror was left on stage during his recitation, revealing his crutch
to the students who consequently erupted into howls of laughter.  What
was the title and author of this story?