One of the best ideas (not original with me) for selecting leaders:

Prior to any selection/election of students for Leadership Team positions:

Let all band members know about the positions you wish to fill (drum major, band president, loading crew, etc.).

Ask interested students to submit a one page statement of their interest in the chosen position and how they wish to contribute from that role. (This is basically a self-nomination.) Privately disqualify those students who do not evidence those traits you wish to encourage in your students. Tell each disqualified student specific qualities that can be developed to qualify them for future consideration.

For those whose self-nomination assures you of their interest in working for the good of the band, conduct any auditions or try-outs required for the position.

Select members based on their performance in try-outs, their vote total, etc.

When all positions are filled, you have written evidence of each student's intent to work hard in the positions they have earned or been elected to fill. Should a student fall short of your expectations, you have evidence with which you can privately confront the student and offer the non-performing student leader an opportunity to correct the actions that are not consistent with your expectations and her/his own written intent.

The entire process discourages students from trivial participation in leadership roles and offers the director opportunities to counsel students toward positive contributions to the organization.

Good luck