First for music ed, learning a new instrument will be helpful. However, music ed admissions and scholarships are driven by audition(s) on a primary instrument/voice. I would encourage him to work to refine his repertoire with the help of his private teacher. Check the websites of the target schools and see what they are looking for in terms of audition pieces. For music ed, he will need to take piano for 1-2 years depending on the school but would be able to test out of it if he is proficient. Once he is a music ed major, he will spend years learning secondary instruments. Even though his goal is to be a High School Band director, many times new grads will be working at the elementary or middle school and wearing different hats. Son was fortunate and is a full time elementary orchestra teacher but an instrumentalist friend is a general music, band and chorus teacher for another elementary school. Speak to his current music teachers and see which schools they would recommend for him. Good luck and enjoy the musical journey.