I have a theory that methods for teaching improvisation (beyond the broader jazz music idiom) arrived late in the history of jazz education. There were high school jazz bands before there were Aebersold albums, and reams of multi-media how-to materal on chord progressions, modes, the Lydian Chromatic Concept etc.
Remember how the jazz big band charts used to come with a “written” “improvised solo” to address this short-coming? How many of you will admit to having played the “suggested solo” in your high school jazz band? Maybe it was because you didn’t feel ready to skate through the changes of “Cherokee” yet or maybe your band director asked you to because he thought it would make the organization look good and help you win the big trophy at jazz festival.
Which brings me to my next observation that there were three basic categories of jazz band director when I was growing up:
#1 Old School — Tends to call his group a “stage band.” Record collection consists mostly Boots Randolph (Yackety Sax) and Elvis. White shoes and belt a must for important concerts.
Old School
#2 Coach — Must win the Festival. Creativity is for cry-babies. Tempos start at 120 = half note and rush up to 140 before the tune ends. Dynamics range from FF to FFF. Record collection consists of Buddy Rich and Maynard Ferguson. Usually outfits the band in monogrammed polyester sportshirts that look “sharp.”
The most important thing you will do this year is bring back the trophy for the T-birds
#3 Our Savior — Can speak with confidence on chord progressions. Knows phrygian mode is not a type of sexual disfunction. Has a lot of Ornette in his record collection. Might call the jazz band a jazz “ensemble” or even a jazz “workshop.” Likely to give you a second chance if he catches you smoking weed on band tour.
Play from the heart brother
Serously though, one of the finest examples of the “Our Savior” variety was Grant Wolf, beloved jazz studies professor at Mesa Community College, purveyor of an excellent jazz scene during his time there and an inspiration to hundreds who pursued the jazz art form.
Chris Fagan Jazz 
Grant was indeed a Jazz Savior for a lot of people. I grew up in a small, very isolated town in New Mexico, so it was truly life changing to discover Grant’s hip musical scene at the NAU high school summer music camp. The single high school in my home town had a very good music program in a lot of ways. We had three “Stage Bands”. Not many high schools can say that anymore. But our charts tended to be heavily drawn from the Maynard and Kenton libraries, which made all the trumpet students ecstatic. Occasionally we played something that swung good, like a Basie chart. I didn’t read well enough to play the “written solos”, so I just tried to improvise. My one year at New Mex State was dominated by more loud, precision type brass heavy “stage band” charts. None of the faculty there knew anything about improvising. So it really did save my creative ass to come over to MCC and get involved with Grant’s program and the many talented students there.