There are more than 20,000 high-school band programs in America, some with as many as 400 members. “Over the past 30 years, their shows have evolved into spectacles that John Philip Sousa couldn’t have imagined,” Burkhard Bilger writes. The top bands have dozens of staff, budgets of hundreds of thousands of dollars, and fleets of trucks for their instruments, props, costumes, and sound systems. “They don’t just parade up and down the field playing fight songs. They flow across it in shifting tableaux, with elaborate themes and spandex-clad dancers, playing full symphonic scores.” Students rehearse intensely, not to play well at football games, but to prepare for a series of fiercely competitive marching-band contests in the fall, culminating in the Grand National Championships, in Indianapolis. The area is “the capital of the new marching-band culture,” Bilger writes, and has two of the country’s most successful marching band programs: the Avon High School Marching Black and Gold...