In a discussion, Peter shares his opinion about playing in the marching band: "Everyone should join the marching band! Making music with my friends is a lot of fun." Which fact best supports Peter's opinion? Students who listen to music while completing homework are often distracted. Students who play an instrument get better grades than students who do not. Marching bands usually include woodwind, brass, and percussion instruments. Marching bands were originally part of the military, used to direct troops on the battlefield.
From the above excerpt the fact which best support Peter's opinion is that STUDENTS WHO PLAY AN INSTRUMENT GET BETTER GRADES THAN STUDENTS WHO DO NOT. This can be inferred from the passage: Peter considered playing an instrument a lot of fun; playing musical instruments is great for brain development. It helps the brain develop neurophysiological distinction which helps students distinguish between certain sounds that can aid in literacy.
I would say that students who play an instrument in a band or group probably get better grades in their other subjects than students who don't. I think that making music would relax their minds and make it easier to learn as a consequence, and also playing in a group or band means doing things collectively and learning teamwork and to be sychronized which should help with other subjects as well.