Mini white boards are a most necessary homeschool item in our household. It is a nonthreatening way to teach a new math concept. We use it daily to teach Spelling patterns. I finally had the good sense to buy a 2nd whiteboard for the 3yo. It keeps her from stealing ours during Spelling. Ours is magnetic so the 3yo can put letter magnets on it for early Phonics lessons. She also draws a lot of sunshines on it:)
We got our boards from Walmart for 2.39. A set of markers was 5-6 and comes in many colors. We've found cottonballs make the best erasers. If it gets really smudgy, rubbing alcohol makes a good cleaner.