Understand I'm a 4A director with only a few years under my belt, but I feel my ensemble plays pretty well in tune. Not perfect, but they're somewhat close on pitch center.
And let me preface this with you'll need some money for my approaches. Both of the things I purchased were purchased through the IMA funds. Band budget didn't spend a penny on what I'm going to tell you to buy.
You need a harmony director (or another pitch-generating device) and a tuner/pickup for every wind instrument in your band.
We use the Korg TM-50 with the Peterson TP-3 pickup. Less than $30 per student when ordered through WWBW. Again, band didn't spend a penny on them - the IMA funds for the district did.
With that said ear training is experiential. YOU must guide them to match pitch. Have them play a note with the drone going and you direct them to match it. It happens individually. When we're setting horn lengths in full ensemble the kids are responsible for getting their tuning pitch to "green light" on their tuner, but the actual part of teaching the ear to match pitch is a guided experience that you must do with them.
This is part of my warm up in the spring when I only have about ~60 kids in my top ensemble. We play part of the warm up, set horn lengths for one section, another part, another section, etc. At the end of last concert season, the first season I adopted the process, it would only take me 15 minutes to warm up and set lengths for EVERY kid in the band hall.
The key to it though is YOU have to help them match the pitch the first time. After that they will slowly start to develop sensitivity to it and mak it happen faster.