“spelling: Word in the English language can be difficult to learn to spell because of many irregular spelling patterns. For example, do, due, and dew are all pronounced exactly the same way but differ in meaning. While English has 44 sounds, it has only 26 letters.
The letter-sound correspondence is essential for reading, as is the sound-letter correspondence for correct spelling. A difficulty in these relationships results in language disabilities.
Spelling a word id fare more difficult than reading a word for several reasons. First, passive (receptive) skills such as reading tend to be easier than active, expressive skills such as spelling. In addition, there are not contextual or structural cues to help with spelling as there are for reading. While spelling can be difficult for average learners, in is particularly difficult for individuals with a weakness in decoding.”
Excerpted from: Turkington, Carol, and Joseph R. Harris, PhD. The Encyclopedia of Learning Disabilities. New York: Facts on File, 2006.