I simply use household cleaner spray (409 in my case). Everything comes off easily. A few spots might need a little scrubbing, but not much. And the board comes out sparkling white.
By Cricket from NC
Although household cleaners may clean whiteboards, they can also damage them too! In fact, 409 can actually cause stripping, which can lead to ghosting (that's when the ink settles in and stains the board). I found some pretty useful information from these two links about cleaning whiteboards and how to address ghosting!