A couple ideas:
1. Make scales a part of your daily rehearsal. The warm-up phase of your rehearsal can easily include scales. I had a band-director colleague who had a daily regime: when the bell rang, the band launched into a series of all 24 scales-major and minor in circle-of-fifths order. He took roll meanwhile. The whole thing took only about 4 minutes.
2. Make scales a part of your audition/seating process.
3. Make their grade depend on assigned scales. This is real, measurable assessment (to use the current jargon). Certainly you don’t mark them purely on showing up.
4. Athletes do calisthenics; musicians do scales.
5. Encourage your feeder school directors to introduce and set the stage for your expectations at the high school level.
There are many scale resources on my webpage. All copyright-free and gratis. These I used regularly in several school systems over several decades.