They can’t detect if you boot into Linux; but they can detect the presence of external storage devices and scan their contents. It is best if you do not plug in your LiveUSBs or disks while the system is [ONLINE] (Meaning while the device is booted into any default operating system)
Chances are if your hardware has not changed; the capabilities have also not changed. I do however have a few tips for you:
DO NOT MODIFY THE DEFAULT OS OR SPYWARE! It sounds like they are now monitoring the files for the software and will now notice if you have disabled it; as your machine will probably be sending heartbeats to a centralized server. You must accept this spyware when operating the machine as intended to interface with your school environment; but you can limit yourself to submitting schoolwork only on it
Boot into a Live(CD/USB/Media) environment of Linux with Persistence. Google it. They can’t detect this without BIOS tampering.
Do Not plug your Live Media into the system when booted into it’s default mode. Your drives are probably being scanned.
Keep a separate media storage device for storing your documents and such.
You can boot into your Linux key to work on school things and browse the web privately. Remember though that you are [OFFLINE] and may be unable to access the school network and will be required to save your work on a different piece of media, shut back down and boot into the default OS again to submit your work.
You may be unable to complete assignments in Linux [OFFLINE] that require you to respond to questions interactively [ONLINE] or otherwise require that you be interactively [ONLINE].