And so breed a generation of coders that think you need to reformat machines every time they exhibit the tiniest of bugs. Lovely. Exactly my point.
P.S. How are you going to install to download and install the OS on the RPi machine in the first place, how are you going to get it to receive updates, how are you going to follow online tutorials for it, how are you going to make sure the kids can't just brute-force passwords or attempt DDoS on the servers using their lovely £20 machines with network connectivity, or spamming the Internet because they "downloaded a project" for the Raspberry Pi that turns them into spam-spewing zombies, how are you going to stop them bypassing filters, etc.etc.etc?
By having decent security on the network to detect and/or block such activity no matter what machine tries to do it - which is necessary anyway, so what have we achieved? Nothing. This is the entire problem with BYOD, by the way - sure it can work, but what you're basically doing is APPLYING SECURITY so that it doesn't cause you legal or technical problems when used from an unsecured machine (which is kinda a daft thing to do, but that's not my problem because I don't do it). A school was fined hundreds of thousands of pounds not-so-long-ago for having a laptop stolen that was unencrypted and had children's reports on it - there wasn't even a suggestion that anyone actually has that data or has distributed it elsewhere or caused any damage from that data leak. We're not even talking highly-sensitive data (school reports usually contain name and a brief summary of their progress from their teachers - not even their address or anything related to medical / psychological problems they may have), and they did all the reporting of the theft as prescribed by law. The encryption (and subsequent password management, and security ensuring the staff member doesn't "unencrypt" even quite harmless data by putting it onto a USB stick and leaving that in their car - which has ALSO been prosecuted) is there for a reason - and to be honest, it causes me problems and I'd love to be able to do without it for client machines.
Fact is, computer systems in schools (and businesses) are like that because they contain data that needs to be protected and which can't be passed off to cloud systems, can't be easily put into the hands of third-parties without explicit contracts, can't be unavailable - e.g. emergency medical information on children and/or required exam coursework for them to work on that happens to come under the DPA. There are legal requirements to store and protect that data for years (and if a kid has a photograph with a name attached to it, or even some information about themselves like, say, a test CV - that's "personal data" under the terms of the DPA, so we're not just talking about things on the "admin" network here, but the "curriculum" network that the kids use too), and doing so in accordance with various laws which mean passing it off to a third-party cloud host in the Bahamas doesn't let you off, and in fact gets you into more trouble.
Even letting a single rogue host onto an unsecured network that can get access to something it shouldn't can be defined as a failure to protect that data (even if it's the kids' own work, on a kids-only network, from kids-only hardware!), and can be prosecuted - which is where basic network security comes in in terms of approving applications and plugins, limiting users, blocking off the Internet, keeping on top of antivirus and vulnerabilities, etc. comes in.
Fact is, there's nothing that CAN'T be done on a properly secured network, otherwise there would be no point trying to secure the network at all (hell, virtualise everything, if it comes to it!). It just has to be done in consultation with your IT people and with due care and process. Thus why I call horse-manure on this particular quote. If security is interfering with your ability to teach ICT, you're teaching ICT badly or your IT people are failing in their job. But if there's NO security at all, in the name of not interfering in lessons, your IT people will be disappearing so that they aren't named on court proceedings when it comes to a DPA violation and your external providers will all have clauses that mean they are immune or that it's your problem, not theirs, that little Johnny's personal details just got splatted all over his friend's Facebook pages, traced to a school dataset).
Want a school that doesn't have basic security applied? BYE!
Want a school that has lessened security because of perceived "problems" on the user end? Slippery-slope into all-users-being-admin areas, and inevitably you'll find holes everywhere that you can't stop without being as strict as the average school network security policy anyway (that's WHY those policies are that strict as a minimum).
Think that end-users are hindered in their use of a properly-configured computer on a properly-secured network? Tell your software manufacturers, especially educational ones, to pull their fingers out and not require admin access, local installation, out-of-date Quicktime and Shockwave etc. browser plugins, in order to show three croaking frogs on the screen and let the user click one of them to be directed to an external website that runs Java plugins and hasn't been updated in years. Then see how "necessary" it was to change security policies to stop "hindering users".