So if you go the route of using an open/semi-open OS for your tablets and mobile devices, like Android, the time will come where you will want to stream video on it or to it. In walks Plex.
To use it, you will definitely need to plan things out. You will need the Plex server running on a machine somewhere on your network. All the content you want to stream will need to be on it. You will need to give careful consideration to that machine and how many clients you want to stream from it. You probably will not have a 1:1 environment, but if you have a few in your classroom (or home), this should work well. For instance, I use Plex on my Sony Blu-Ray with Google TV, and also on my tablets. Works great to show photos, stream videos, and just be cool. I can envision a classroom with a Google TV box or just some tablets, and the teacher assigning videos to the students. Or student created videos. Definitely, though, take time in thinking about it, planning it, and moving slowly with the process.
Get Plex on the Android Market at: https://market.android.com/details?id=com.plexapp.android