This is a wonderful site to "plug-in" your student's vocabulary (in any subject) and allow the student to learn their words through use of flashcards, games and tests. I was even able to email the link to my students via their facebook accounts.
This site allows the parent/teacher to post a spelling list for the student to practice. Again, it uses games to help them learn the new words. On spellingcity.com, the student can also hear the word spoken and used in a sentence for context.