The single most helpful thing for learning to spell is to read — to read LOTS and lots of books. Seriously. Reading well-written literature is more beneficial to language development (writing, spelling, grammar, etc.) than any language curriculum you’ll ever use with your kids.
I wish people would “get” this … but it’d probably put a lot of curriculum companies out of business if homeschoolers came to understand how good spellers and good writers are actually created. 😉