It's already been posted here but I thought I would mention it again.
For teachers who have students that need to prepare for spelling tests or get extra practice,
www.englishquest.com.tw has an excellent program that allows children to practice more than 4000 words. It uses a game setting so it is fun and it also provides excellent feedback. Give it a try and if you find it useful, encourage your students to use it. Remember, it's FREE!