Spelling is often a difficult subject for children. Sometimes it is because the teacher assigns vocabulary words instead of true spelling words. Spelling words should be based on spelling patterns.
So before I give you some strategies on what you can do to help your child, can you give us some more information.
Sampling of a week's spelling words
Number of words assigned
Types of assignments (write words 5 times each, use words in a sentence or story)
Is the problem with getting your child's homework completed or his performance on the test?
Once we have more information, we can better help you and your son out.
If you have the ability to work with his interests to get him to work on his spelling that would be great.
I have one student that comes to my center (tutoring) that loves legos but hates spelling. I created a set of duplos (for the size) of all of the letters and blends that he could possibly need. He now creates his words out of the legos and has greatly improved.
The teacher has even allowed his mom and I to sign off that he has completed the assignment rather than him writing them.
His grades have improved!