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, it has to be enabled for all devices.
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]
Allowing devices
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.
Using WebUSB
Another option to mitigate the issue with Bitlocker is to make use of the WebUSB functionality in some modern browsers
Further information
exclude certain usb hardware id from BTG policy