And this is one teacher who'll sign the declaration that it's being used in the course of work.
Illegally of course
Where does it say in your contract that you have to carry anything anywhere?
Fair play to you for doing all the lifting and carrying but if it's not part of your job then you are doing it voluntarily and if you are doing it voluntarily then you are not entitled to tax your vehicle as a commercial vehicle.
Don't get me wrong - I think it's a stupid law but being in breach of a stupid law is the same as being in breach of a good one.