I'd say, depending on how LOW they are, focus on their phonics and sight words first (back to the basics). I use a spelling inventory test. It is a list of words that you ask the students to spell and it shows which orthographic features they have and which ones they are lacking. For example, they might have the wr, th, sh, ch but they lose it when they have to double the final consonant when adding ing to a short vowel word like "hopping." There is a primary spelling inventory test that goes up to 3rd grade, I think. And then an Intermediate spelling inventory that goes up to 7th, I believe. They help find the gaps in the childs spelling abilities and gives you an idea of where to start teaching them. Hope that helps! Ahh.. just remembered the name of the book "Words Their Way." GREAT BOOK!!!
First, check master of sight words. Then go through the list of 500 most commonly used words in children's lit (I don't know where I got it, but it is in the back of books like Words Their Way). Assess for phonics weaknesses. Go over spelling patterns.
