Small Aircraft; Low Wing; 1 Eng; Fixed Gear
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 10
Communication Breakdown; Distraction; Training / Qualification; Human-Machine Interface
ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance
Human Factors
I was CPC [Career Professional Controller] training an FLM-IT [Front Line Manager-In Training].  We had a Small Aircraft (Aircraft X) overflight at 090. Air Carrier X (Aircraft Y) departed.  Trainee climbed Aircraft Y up to 100.  There was plenty of room to turn Aircraft Y; so I did not have trainee amend altitude.  But then FLM-IT got distracted with traffic on the east side of the airport.  I prompted trainee to turn Aircraft Y.  FLM-IT keyed up; so I thought that is what FLM-IT was doing; then FLM-IT talked to other aircraft.  I still felt FLM-IT had time to fix it; so I prompted again a second time.  FLM-IT keyed up and talked to another same Air Carrier X (Aircraft Z) on the east side of the airport and not Aircraft Y that I was referring to.  Finally the third prompt FLM-IT talked to Aircraft Y.  I knew it was close to a loss of 3 miles; but thought FLM-IT turned Aircraft Y early enough; but it was not. When discussed after the session; FLM-IT did not hear me say to turn Aircraft Y. Which could have been because I was talking thru a mask and communication is muffled.When training I need to use full call sign with the numbers when telling the trainee to do something.  I kept saying turn Air Carrier X. We had more than one Air Carrier X that we were working.  So I need to be more specific. I can also just key up and turn the aircraft myself which I normally do if I feel like it is warranted.  I honestly thought she caught it early enough.
ATC TRACON instructor reported miscommunication with trainee resulted in an airborne conflict during a training session.