Brass,
I hear your pain man. At all of the places I have ever taught I have always had at least a portion of the Front Ensemble similar to your's. It is difficult, but unfortunately common. It seems that a lot of beginning band directors either dont know percussion technique, or dont put enough emphesis on instructing it properly. Unfortunately the only way to correct it is to keep beating it into them. Also you should suggest that they start taking lessons from a good private instructor, that will help a ton.
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Scott M. Sheets
Percussion Instructor
PMA Sinfonia AX
Formerly PNHSTech