Inside of the rock there is some type of fossil and it looks like a tiny tooth. Whatever this is, it's very interesting and doesn't make any markings when drawn with. It is white and yellow, almost clear. It looks like some type of crystal but I don't know. I found this at my primary school in Australia 3 years ago. Please help me figure this out.
Your stone is almost certainly a clear opal. I see no sign of opalescence in your photographs, which would make it of very low value except for the fossilised tooth. Fossils are occasionally found in opal. When they are found in amber (a completely different mineral) they raise the value of the specimen, so I expect it's the same with opal. Opals are formed in chalky sediments at the bottom of the sea which solidify into rock over the course of millions of years. Chemically they are hydrated silicon dioxide, and have a high water content which is responsible for their opalescence, but some opals are clear or milky. I'm no expert on opals, but even with a fossil tooth inside it I would think that without any opalescence in the stone it would be of little value.