Quote Originally Posted by birdgirl73
When I was teaching, the word "separate" often gave kids a lot of spelling trouble. Which is why the little mnemonic saying "There's 'a rat' in separate" came in handy.

I don't know the single most commonly misspelled word. But I found this about the most common 100 words:
http://www.yourdictionary.com/library/misspelled.html

Well I was going to say 'weird' was most mispelt, but there's no point now.