The screenboard is a great accessory to both the reading and writing resources available here. There is much evidence that some children learn better kinesthetically. The screenboard provides a kinesthetic strategy that is both easier and cheaper than how it has been done in the past. Instead of keeping track of individual sandpaper letters or a dealing with a messy sandbox, just use a screenboard and a flashcard insert.
Please take a look at the pages linked below to get a better idea of the value of the screenboard. Read the kinesthetic learner page if you have a child who learns this way. There are some great suggestions.