The basics of it are that you need to have a comprehensive scope and sequence from beginner band through second, third, fourth, and up. (I say years rather than grades because I believe strongly kids in 7th and 8th grade should have the right to start beginning band too)
In short, you need to work with your vertical team, figure out what the "need to be able to do" stuff for your high school kids is, and plan backwards. For example, if your high school kids only "need to know" seven scales and a chromatic, as is common with ATSSB school auditions, are you going to spend the time drilling all twelve majors in eighth grade?
(Yes, they need to know them all if they're going to college as a music major - but the VAST majority of kids are NOT doing so. The ones that want that level of preparation can be scaffolded in and differentiated appropriately - see what I did there?)
Meet with your full director team and plan it out. If you *are* your full director team, then talk to other districts nearby to see what their expectations are - or email directors of programs you admire to ask what THEY expect out of their programs.