Original sentence: A few scattered show choirs exist internationally, most notably in Canada.Growth started heavily in the Midwest following the 1950 founding of Indiana University's Singing Hoosiers, and in [[Southern California after the 1962 founding of the Young Americans in Los Angeles.Many middle schools and junior high schools each have a own show choir as well, particularly throughout the American Midwest.Show choir began as an activity in the United States during the mid-1960s, though cultural historians have been unable to determine the true "first" show choir.Show choirs also exist at the collegiate level, albeit in far smaller numbers than their high-school counterparts, and in most cases adopting a slightly different format.Show choirs seldom have more than 50 singer/dancers
Edited sentence: A few scattered show choirs exist internationally as well, most notably in Canada.Because show choir is usually an optional high school activity and the size of high schools are limited, show choirs seldom have more than 50 singer/dancers.Growth started heavily in southern California thanks to the Young Americans founded in Los Angeles in 1962, and in the Midwest thanks to Indiana University's Singing Hoosiers founded in 1950.Many middle schools and junior high schools now have their own show choirs as well, particularly throughout the American Midwest.Show choir began as an activity in the United States during the mid-1960s, though given the artistic nature of its core, it's impossible to determine a true "first" show choir.Show choirs also exist at the collegiate level, albeit in far smaller numbers than their high school counterparts, and in most cases, in a slightly different format