Your band may end up being "stock market band." Some days are better than others, but for the long term are they growing and are they getting better?
A wise older director told me once that teaching JH Band is really about "putting rehearsals together." You can assume there will be a dip on Mondays, but if you can have a good rehearsal, then you do everything you can to make Tuesday great, too. Then, the goal is to have five in a row, but also know that they are JH kids and sometimes two in a row is an accomplishment.
You do need to hold their feet to the fire, too. Find something you can take away from them and hold it over their heads. For me, I had a group that rehearsed right up until lunch time. Every time I had to wait on them to be quiet, I told them I would add that time to rehearsal. The first day I held them 4 minutes after the bell, they started to "get it." It also ensured that I got all of my rehearsal time. Obviously, your situation may not work this particular way, but you may have a corresponding strategy you can deploy.
Lastly, celebrate all of the "wins!" You get more flies with honey than with vinegar, so finding an opportunity to bring a piece of Halloween candy for some accomplishment can really turn some kids on. A lot of classes won't have a natural cause and effect (other than grades). You can be the teacher that they get that little dopamine shot from. Once they realize good work and behavior will be rewarded in your class, you'll get more of the work and behavior you want. (Be sure to explain the direct relation of why the student is getting the reward, so they can repeat the behavior.)
Good luck! When all else fails, pretend to be a clinician!