I think that he is making a valid point.
If you went into a computer suite with 30 already wired in computers it would take ages to get the pupis to unplug the keyboards mice etc, (even if they could as most keyboards/mice etc are locked to the cases to prevent theft) find a plug socket for the PSU etc. Ecen then a fairly high proportion of the class would have forgotten their SD card etc etc.
The idea of getting thirty pupils to put the PC,s back together at the then of the lesson in a state where the PCs will just boot in anything less that 10 - 15 minutes is a laugh. If my school is anything to go by you the teacher have to check each pc individually and sign that they are working OK before leaving the classroom.
Overall this would take half the lesson or more.
If you are thinking that the school would dedicate a room with 30x RPi all set up ready to go then I think this would be a very rare school indeed, they just do not have the room for something that will be used once in a while.