If you’re using the Apple TVs in your classrooms to show videos—especially HD videos with a lot of motion—you may find slight or significant lag in the image coming from the projector, especially if you are showing the videos from your Retina MacBooks. If your big screen video pauses, breaks up or just looks kinda jumpy, try switching to the extended desktop mode under AirPlay, on your toolbar at the top right of your desktop.
Note: This has nothing to do with the Internet. I’m not talking about signal delays that might come from online streaming sources, I’m referring to complete files on your computer that still seem to stutter and break up.
Basically, choosing the extended desktop option does just what it says, it extends your desktop off to the right hand side, rather than mirroring the same desktop.
I think that by not mirroring the display, your MacBook only has to process the video once, rather than twice—thus taking some of the pressure off the graphics card.
This solution has been working for me, please let us know if you have any other suggestions!