What makes a good speller (or a bad one)?

In the context of the National Spelling Bee, Brenda Rapp, lead author of the Brain study on the ‘Neural bases of orthographic long-term memory and working memory in dysgraphia’ explains how some people’s brains retrieve words (or don’t) and how we manage to get them out (or not). So what is it that separates the spelling stars from the dictionary-deficient?