FWIW, while researching soapstone, I found out that in rare instances, soapstone can contain asbestos veins running through it. Because of this, I looked into the danger of asbestos being consuming orally, and, from I can tell, there is none. It's only when inhaled that asbestos becomes a carcinogen.
For the customer, an asbestos containing stone poses no threat. For the employee, though, I would take a few precautions. Rather than using wood to launch and metal to turn and retrieve, I would probably using wood for both, making sure to have two separate wooden peels, so the cooked pizzas don't get defiled with raw flour.
I would also clean the decks with the softest possible brush. I did some research on soft brushes when I first started looking at soapstone, under the assumption that the soapstone I'd get would be talc-y and scratch easily, but the soapstone ended up being much more durable than expected. Anyway, extremely soft non metal brushes don't stand up to heat. Thin bristle brass brushes might be the answer, but I'd perform an exhaustive search to make sure there's nothing better out there. The last thing you want to do is use a brush that scrapes the decks and sends asbestos particles airborne, which, in turn, causes them to be breathed in by your students. Inhaled asbestos is a huge deal.
Lastly, I'm sure your aware of this, but if you continue using these decks, don't ever say the word asbestos in front of a health inspector, as they'll shut you down in an instant.
If you want to breath a little easier (literally and figuratively) and get rid of the asbestos decks completely, you should be able to approximate their heat spreading effect with firebrick or fibrament, although the firebrick could involve adding additional support structure. You can also help even out hot spots with a layer of steel plate underneath the hearth. If you do replace them, take IR readings of the decks and time the pizzas carefully. The temp and time will give us a better idea of the conductivity of the material, which, in turn, will help you choose the best material to replace it.