Airplay is simply not working

My ipad and Apple TV are right next to each other, on the same network, signed into the same icloud account... I can see the apple tv in my screen mirroring pulldown menu. I select it and get the message "unable to airplay", no explanation, no error code, just a straight no answer. This is so frustrating, I cant get my kids school on screen!! I've followed all of the directions to a tee.