The secret is to teach them what "in tune" sounds like. MSers have played out of tune most of their lives... so they will naturally gravitate to that sound. It's a bit tedious at first to use a warmup and go down the line and tune each kid with the drone... but it will be a fix they remember and be able to reproduce. I often say "playing sounds like you disappear in the band sound". Kids will often start in tune and then adjust out of tune because they can hear themselves more... thinking they are contributing more.

Kevin Russell