Although harmonica bands and orchestras have generally been forgotten, the harmonica was one of the most popular musical instruments from the 1920s through the 1940s. Its cheapness made it an ideal instrument for teaching music to children during the Depression, and the harmonica youth orchestras were influential in instilling discipline. In the years between the two world wars—a period called the "the golden age of the mouth organ in America"—sales of the tiny, inexpensive instrument increased dramatically. Bands of har-monica players became famous on the vaudeville circuit, on radio, and in Hollywood films; whole orchestras of harmonica-playing youth were organized in cities all over the United States, and public schools offered harmonica instruction courses. The craze finally hit its peak in 1947 when the Harmonicats' rendition of "Peg O' My Heart" became the number one hit of that year.

It all began during the Boy...