MacBook and iPad items to check: 

• Verify iPad and/or MacBook operating system up to date. 
• iPad select Settings app > General > Software Update
• MacBook select Apple icon (top left corner) > About This Mac > Software Update (middle of dialog box) Update info here
• Turn Wifi off then on. This is helpful when you have changed classrooms or buildings. 
• MacBook: If someone else can connect to the Apple TV and you can't, do a shut down and turn computer back on. If your computer still can't connect, but others can, place a IT help ticket. 
• iPad: Do a soft reboot of your iPad. Press the home screen and power button down at the same time until the white apple appears on the screen. If you still can't connect, but others can, place a IT help ticket. 

Apple TV items to check: 

• Verify Apple TV is awake, the white light on the front is illuminated. If not you can wake it by pressing a button on your Apple TV remote.
• Verify Apple TV Airplay is on. On Apple TV remote: Menu button > Settings > Airplay, should be listed as on.
• Restart Apple TV: On Apple TV remote: Menu button > Settings > General > RESTART (DO NOT DO A RESET) 

None of the above resolve my issue: 

You are considered down and can't present at all, place a phone call to the HS office and ask to have IT contacted by radio for help.