how to teach a fourth grader spellings?

Answer 1

I don't think anyone has found a better way than practice, practice, practice. Write each word 10 times, paying attention to the order of the letters.

This site has four rules that everyone should know.

http://grammar.about.com/od/words/tp/spellrules.htm

Answer 2

Another thing that worked well with all my grandchildren is "pyramid spelling," as they called it. Here's an example:

a
al
alt
alth
altho
althou
althoug
although