I'm a middle school band teacher, and I match students to instruments by testing them on various mouthpieces. While most children demonstrate aptitude on more than a single instrument, there was one boy who was having difficulty on every one he tried, and he was becoming disheartened.
Finally, he found success on a tuba mouthpiece. He was so happy that he asked to call his mother.
"Mom, guess what!" I overheard him exclaim. "I tested positive for tuba!"