Storage problem: "Other" taking up all space

Question

To situate my context: I'm IT-specialist at my school, where we have an 1:1 iPaddeployment for about 700 pupils and 100 teachers. Most of the pupils use the 16gb wifi version, purchased near the end of August '12. Over the last month, we've have about 20 pupils (and not teachers, which is peculiar) with the folowing problem:
- iPad shows error "Not enough storage"; when checking Info, the iPad suggests they have 0 bytes free space
- Pupils' iPads contain not too many apps, at least not enough to take up +10gb
- Upon connecting the iPads to iTunes, "Other data" takes up 8, 10, 12 ... gb of space;
- There is no way to overview or analyse the contents of this data;
- Taking an iCloudbackup with the standard 5gb of free space is impossible;
- Taking and restoring from a manual iTunesbackup is also not possible: when wanting to restore from a freshly taken backup to the same iPad, the iPad gives an error, saying there is not enough space to put back the backup. Strange, seeing as this suggests the backup taken is bigger than the actual capacity of the iPad.
What we have tried:
- Slimming down the backup to just the necessary and even standard apps;
- Deleting apps before taking the backup;
- Emptying apps before deleting them from the iPad (we've suspected a few videodownloadapps for leaving chunks of (half-)downloaded videos, to no avail);
- Empyting Camera roll;
- Taking camera roll out of the backup;
- Emptying Mail / iMessage messages;
- Logging in/out of iCloud;
- Soft/hard reset;
- Connecting to iTunes;
- Checking/unchecking the "Open iTunes when connecting this iPad";
- Checking/unchecking the wifi synch through iTunes;
- Using iExplorer, iToolbox to manually erase faulty files (nothing can be traced);
- Restore trough iTunes using local backup;
- Resetting all network settings;
- Putting iCloud backup on a different iPad;
- Updating iTunes
- We've contact the AppleCare pay-per-incident, the problem wasn't known to them so no solution could be given
- Talking to some Apple Geniuses in Regent Street and Covent Garden, the problem was unknown to them
- Updating iPads to 6.0.1 or 6.1
What we suspect:
- Eventually we thought the problem might be with the videodownloadapps. We've discoverend in two cases an iPad where, when you browse with iExplorer, video files were found. Those files were about 1,5gb each and there were 4 copies of each file. Deleting these manually did not work.
- We use a custom made inhouse app to provide books for our pupils. In order to install these apps, a profile needs to be installed from the publisher's webdsite before installing the acutal app. Another one of our publishers works with an offical app (https://itunes.apple.com/be/app/silverboard/id556871870?l=nl&mt=8) and is virtually an upgraded webapp.
- An odd thing is that, when communicating with other schools abroad, not a single one of them has experienced this problem.
- An option we have considered was that it might be a hardware related problem. We have, however, ruled this out because the problem occurred as well with 32 and 64gb iPads, with wifi and 3G models and with models bought in different periods of time.
What we could like to know:
- Can an app be allowed to write into "Other data"?
- Can a profile allow an app to write in "Other data"?
- Is it possible when deleting an app that has been installed through a profile, leaves behind chunks of data? When deleting the publisher app mentioned above
from the iPad, the profile still exists, so could some of the data be left behind as well?
The only "solution" this far is connecting the iPad to iTunes, transfering all purchased apps and data, restoring the iPad as a new iPad and then manually synching. Needless to say, this isn't a solution or explanation to the problem and terribly time inefficient. At this point, we're juggling with making instructional videos and/or a keynote, telling pupils how to restore, but again, I'm not satisfied that this is the only solution we offer them. It needs to be resolved.
If anyone would have any ideas - or even better - a solution, please do share.
Many thanks
Kristof

Answer 1

You can get a inventory of your hard drive content in more detail than the Mac OS provides using Disk Sweeper.
http://omnidisksweeper.en.softonic.com/mac