I've been giving DS5 spelling words lately, to get him thinking about basic building blocks. Some are short, some are longer (a recent longer one was "debilitated"). Every time we do a new block, I have him recite spellings of at least some of the previous ones. I also do not hesitate to throw in spelling words he doesn't have in his vocabulary yet, if they share a common prefix, suffix or base with others in the set.
I've been thinking about printing out the sight-word lists up through fourth grade or so and just having him plow through them for spelling practice in the short term. He is remembering spellings from his reading anyway.
