You need to have every student use personal tuners with a tuner caddy on every stand. If they can "see" it in tune, they will better be able to hear it in tune, and their ears develop by leaps and bounds. You will notice a huge shift in your pitch center of your band by using personal tuners. It saves so much time tuning in class with them!

I also recommend harmony director drones alongside tuners and matching the drones.