Spelling Dictionary?

I have two students who really struggle with spelling, which is a whole other post! But my older ds is going to be taking an IEW writing course in our co-op this fall, and I am wondering if a spelling dictionary would help him. I would like him to have more confidence and be able to “help himself” when he doesn’t know the spelling of a word. I’ve heard of spelling dictionaries, and that they are supposedly easier to use for spelling without all the definitions, etc, in a normal dictionary, but I’ve never seen one. All the ones I’ve tried to look at on Amazon don’t have “look inside” photos, so I’m not sure how to choose one over another!

Has anyone had success with a spelling dictionary? If so, which one would you recommend?

Thanks!

Anne