Band teachers, as soon as your students know a major scale, you can teach them to read simple chord changes. By showing them how to put a melody over chord changes instead of just giving them a B flat blues scale and letting them have at it regardless of the changes, you can change their future! Yes, it’s easier to just teach them a blues scale, but they’ll plateau. Give them a good foundation now!
I did this with my beginning bands at the end of their first year. I would even walk around to each student and point at the measures as they went by. Below is a video demonstration using the first few bars of Freddie Freeloader. Beyond just switching to E flat 7 after four measures of B flat 7, I have the student choose which two notes they’re going to play as the chord changes. It’s imperative that they experiment with melodies as they move from chord to chord instead of thinking of each chord as a separate entity on which to improvise in that key.