Hi there! I saw your post, and was hoping someone would reply. I am a K12 Inside Sales Rep here at Aruba and know that there have been a number of districts that have done what you want to do. I can connect you with one of our Solutions Engineers if you would like.
Meanwhile here is a quote from one of our folks in California:
"The answer is yes, it is possible and we did in with the City of Sacramento and we are replicating that with Twin Rivers School District. In most cases we used outdoor Aps for that, put the premises are valid for the IAP-215 as well. There are a few possibilities in terms of the internet uplink on the Bus, but the most basic option would be attaching a compatible LTE USB modem on the IAP’s USB port and using that as your regular internet connection. In the projects we worked on we usually had an external device acting as the internet router (it could be our SD-Branch gateways or something like a Cradlepoint router)."
I hope this helps! Let me know if I can connect you with someone one on one!