A long time ago when I was still a school teacher I was shown a really useful way for children to create their own spelling books. There's a fine balance to be struck between letting a child write without correcting any spellings at all, and correcting every single spelling!
To make these personal spelling books I used old vocabulary books, although folding and stapling lined paper to make a little book would work just as well. I drew a vertical line down the middle of each page and labelled each page with a letter from the alphabet in both upper and lower case. w and x share a page and y and z share a page in our books.
When the child falls upon a word they don't think they can spell they start sounding it out, decide what they think the initial phoneme is and find that page (with a large enough book all the phonemes could be used rather than just the letters of the alphabet) and then have a go at writing the word on the left hand side of the vertical line. They show it to the teacher/parent/helper and they either give it a tick if it is correct or write it correctly on the right hand side of the vertical line if there is a mistake.
Sometimes a child will get the initial phoneme wrong e.g. they sound out 'enough' and on the page for i they write 'inuf' - simply write 'enough' next to their attempt and also enter it on the page for e so that when they start to remember that 'enough' begins with e they will be able to find it again in their personal spelling book.
I have recently started getting my girls to keep their spelling books in their pencil pots so they get used more often!