2. If you have crap horns, they'll USUALLY make a crap sound. If your kids are playing on ISOs, they will never make the sound that a professional level instrument will make. They can make decent sounds but not great ones. In this, mouthpiece/reed is key.
If your kids aren't playing on quality and appropriate mouthpieces, you're shooting yourself in the foot right off the bat. Make sure your clarinet players are on quality equipment and appropriate reeds. Same with saxes. Trumpets need to be on a mouthpiece appropriate to their physiology. Don't trust ANYONE who says that brass players are a one-size-fits-all proposal. For example, some trumpets should be playing on a 7C, some a 5B, some a 3C, some a 1.5C, some an 11B, some a 3B ... find the one appropriate to them. Yes, even into high school. Same with horn, trombone, tuba, euphonium. Same with woodwinds. Not all of your clarinets will have the best results with a 5RVLyre, or 5RV-13. Some need a Fobes Debut. Some need a Vandoren B45. Find what works best for THAT kid.
3. Once you have your kids on good/proper equipment, or even if you don't, stress proper tone production. Lots of breathing exercises and air flow. Work chorales. Work flow studies and long tones. Get the kids to concentrate on making their best tone at all times no matter the technique. Never slack off on expecting tone, tone, tone. Modify your grading policy to emphasize tone over right notes and rhythms. Equipment isn't the end-all-be-all, but it will make this part much easier, since you're eliminating variables that could cause discrepancies in tone production.
4. Give your kids examples of quality tone. Have recordings available (purchased and obtained legally of course) on Spotify playlists and/or SoundCloud. Amass a collection of quality tone producing professionals that they can listen to. Sir James Galway on flute, Martin Frost or Robert Spring on clarinet, etc. Have the kids search for playlists. Wind players develop their own ear for tone by listening to other high quality players and attempting to emulate it. If the only sounds they ever hear are bad ones, then they'll never learn what a good sound is.
This doesn't happen overnight - but it can happen in a year or two. Maybe a semester if you have dedicated kids.
: I am a young teacher, I am in a region with
: some really top-notch bands. How do I get
: "that sound" from my kids?