Light aircraft flight instructor reported an NMAC with another light aircraft on final approach to PCW. Instructor noted that he inadvertently had the wrong frequency selected in the radio; and was therefore not in contact with other aircraft operating at PCW.

Narrative

On the morning of Day 0; I was conducting a training flight with a private pilot student. The student utilized his checklist; and obtained his AWOS weather on the COM2 radio; and had the airport's CTAF frequency in standby. As the student was a new student that I have not introduced to radio communications yet; I made the departure call when we departed on Runway 27; but I failed to notice that the AWOS frequency was active and that the CTAF frequency was still in standby. I had the student fly a normal traffic pattern and while on the final approach leg; I noticed a high wing aircraft that appeared to be going around from Runway 9. I took controls from the student and took evasive action to avoid a collision. I then noticed that the CTAF frequency was still in standby; so I set it to the active position and continued the flight without further incident. I believe that the other aircraft was on an instrument approach; as there was no traffic on the ground when we departed [Runway] 27 just a minute or two prior.I believe that the primary cause of this near miss was my failing to verify that the radio was set to the proper frequency after having my student obtain the airport weather on the AWOS. It was certainly a learning experience for me as a new instructor; as well as for the student in regards to the importance of checklist discipline.