I think that is part of the reasoning behind requiring some minimal competence on a piece. When everyone does some minimal practice, the whole band or orchestra is elevated and there is group pride. There are district-wide bands and orchestras at both middle and high school levels and the support for them stems partly from the results observed at individual school bands and orchestras over the decades - when one or more students earn spots in these, their classmates are motivated to improve as well. Of course, I am in a district of well over 100,000 students with a couple of dozen middle schools alone.