The Down and Out line of Mounts solves this problem by allowing schools to mount the Flat Panel TV above the whiteboard right in the front of the room were it would be most effective. When you need the TV you can simply pull the TV down to a better viewing position. When finished, the TV is easy enough to lift back up to its top position. The pictures show a couple examples of the Down and Out Mounts being used in a classroom in California. The TVs in the pictures can be pulled down much farther then what is shown.
https://www.dynamicmounting.com/pull-down-tv-mounts-for-the-classroom/