Unlike reading spelling is a sequential skill. We tend to avoid the importance of this when the kids do spelling work. They do crosswords and other supposed spelling activities which do not address this important facet. When we spell a word we need to know which letter comes first and what comes next. I highly suggest having a child do their spelling work practice auditorially and orally mainly and then finally moving to written. For example - tell them the word and spell it out for them so they can hear it and not see it. Have them repeat it orally and spell it out orally. After lots of practice this way then move on to dictating the words and having them write them.