Instead of repeating yourself a bunch of times spelling the same words to your students, why not try a spelling dictionary? It's a small 14 page - front to back - booklet for your students to keep in their desks.
There are words already typed out and spaces for more words to be written down. Not only will this end the constant "How do you spell..." for the same words over and over again, but it'll also help your students gain a little bit of independence.
For higher grades you can give them the first three letters of the word and tell them to look it up and write it in their books. For younger grades you can write the word in for them as well as on the board for them to copy down.
With the fun alphabet lettering, this is a cute little book that'll be used a lot!
Included in this are individual pages for each letter - X and Y are the only ones who share a page - and a cover for the booklet.
Enjoy! And be sure to visit my blog at: http://fundamentalsoffirsts.blogspot.com/