I agree with Townsend above, its the software that really differentiates many of the screens. Look at what software you have previously used. You don't have to continue to use the same but it is worth checking to see if any new software you are going to potentially use can open other software files natively. Another thing to consider is how the screens software will integrate with other technology you have in your classrooms. These are things like visualisers, iPads / Tablets and voting systems. Finally I have seen some screens that come with multiple separate software applications where as others combine the similar applications into one integrated solution. Its just something to consider from a useability and training point of view. Hope this helps.
