During most of my public school teaching, part of my duties involved teaching beginning and second level band students. That is still my specialty, but I have had private students continue with me into the high school and even adult level. I often find that band students are already in a school band or are planning to do so. It usually works best if we go ahead and use whatever band book or other music that the school is using. I often supplement that by having students pick out other solo repertoire that they might want to play. Buying music online is usually easy and affordable.