Fun "flashcard" site (with some energy burning activities built in). Site would best be used when a family member works with student, in order to correct and provide the word if unknown to student. You will need to sign up for the free 21 day program.
For students needing to practice addition and subtraction fluency, there are links to both at the top of the page. Great website to practice. Have students use the flashcard option first and then a game. Go back and forth between flashcards and games.