Beretta PX4 C 9x19mm, Walther PPX, SIG Sauer P229R(CPO)...
For general range use or as a loaner, I'd highly suggest a 9x19mm mid size pistol like these brands; Beretta PX4 C(constant action), a Ruger P94 or P95 DA only, a SIG Sauer P229R DAK(CPO or pre-owned), S&W SD9, Walther PPX.
A simple, well engineered hammer fired DA only pistol will have few parts to break, be safe with new range students and last a long time.
The SD9 is a low cost option & is striker fired but each trigger pull is the same. The PX4 C & the new PPX have DA only systems but reduced/smooth pulls.
I owned a NIB PX4 C 9mm in 2009 with 0 problems. Used or LE trade in model SIG Sauers; P229/P226 may be found too. The stainless steel Ruger P series 9x19mm can hold up to wear from range shooting. My friend owns a P89 model that is still very accurate.
Whatever 9mm DA only pistol you select, use the KISS method with new students & teach them to be safe with firearms.