Out of all of the Airproxes I have reported only 2 I have been involved in were non-instructional. All others (probably around another 6 reports Ive made...) were all on instructional flights....where I had right of way. But that aside I suspect the airprox wouldnt have happened and I would have spotted the conflicting aircraft earlier had I not been instructing at the time.
To be honest thanks to radio you dont have to look at the person you are talking to all the time...and Im as much head out of the cockpit as I can be, but the workload on the instructor is considerable; monitoring of hands,feet, flight log, nav, radio, etc etc its an amazingly high workload environment. We arent superhuman so something must suffer, and the lookout is certainly going to be impacted.