I disagree with using a striker model like a M&P, XD or Glock.
With a hammer fired pistol, new(untrained) students can see where the hammer is & learn that the hammer must strike the firing pin to discharge the weapon. As some LE trainers teach with DA revolvers, they can train to feel the firing hand thumb on the pistol's hammer to make sure it's down.
For a range pistol, I'd use; KISS; Keep It Simple Stupid,
A used stainless P94DAO or a CPO format SIG-Sauer in DAK(Double Action Kellerman) would work fine. HK/LEM models could work too, but even used pistols(cost) are up there.