If you are using BitLocker as a way to enforce a policy that all USB removable drives are encrypted or disabled, you will not be able to access the micro:bit.
Microsoft advises that there is no feature to conditionally provide BitLocker encryption on removable storage – either you require it for USB attached (i.e. removable mass media) storage, or you don’t.
So, to work with the micro:bit, the teacher would have to ask their IT Admin to turn off BitLocker removable storage encryption. [Source: Microsoft, 21 Oct 2016]
A workaround is to exclude all USB devices from connecting unless specifically on your allow-list (micro:bit, keyboard, mouse etc). Endpoint encryption has to be turned off for the micro:bit to work.
If you are using policy enforcement software other than BitLocker, you might be able to provide an allow-list based on the devices USB VID and PID identifiers, although specific policy enforcement software may or may not support this allow-list by VID and PID.
Another option to mitigate the issue with Bitlocker is to make use of the WebUSB functionality in some modern browsers