Well, technically it's a salt grinder. I couldn't help buying this for the classroom. I put it on the play-dough table (we make our own). It's a little large for their hands so it takes some effort and a little ingenuity on their behalf to get it to grind. But grind they do! All the salt dries the play-dough out so we have to add more oil and water, which is fun too.
It makes for a great coordination and hand strengthening exercise in addition to a fun kitchen chemistry lesson to boot! The end!