When I began using Sonlight's literature-based approach, I asked this question. I was working with mid-elementary students and part of the Language Arts exercises was to dictate a passage taken from their Readers. Thankfully, I persevered through the early weeks, and then it dawned on me what we were gaining through the use of dictation exercises.
What is the whole purpose of studying Language Arts? To learn to effectively express yourself or to take what is spoken and record it in writing for another to read and comprehend later. One of my students was the type of child who doesn't like to spend extra time doing what he has already mastered, but even he began to see that through dictation he was practicing all aspects of Language Arts skills - capitalization, punctuation, spelling, grammar, and handwriting. Writing from dictation allows your student to concentrate on the writing process without having to compose original sentences. An added benefit was that he was learning about sentence structure through examples from skilled authors. This is actually one of the methods that Ben Franklin used to improve his writing skills.
There is an added benefit for you, the parent - you will improve your skill in reading aloud. When giving dictation, you must use your vocal intonation to help your students hear the punctuation.
Sonlight encourages younger children - those who have not yet mastered handwriting comfortably - to do copywork, rather than dictation. This gives them the same exposure to all aspects of Language Arts skill while removing the pressure of taking auditory information and transforming it to written. As they become more skilled in spelling and handwriting, you can begin to wean them off copywork and into dictation.
Dictation can also benefit your child's spelling skills. When you dictate a passage to your child, present it in phrase lengths that are appropriate to his age and readiness. Have your child repeat the phrase and begin writing. Do not offer help in the writing process - let your child commit his own mistakes. I recommend not even watching what your child is writing as this can cause him to focus on your body language for signals about his performance, rather than concentrating on what he is doing. Allow him to pause when spelling an uncertain word to consider various alternatives or recall the spelling rules he has learned. He should feel free to think through the spelling process. When the full passage has been dictated, have your child read his writing aloud to determine whether he is satisfied that he has spelled everything correctly, as well as using capital letters and punctuation properly. As soon as your child has completed proofreading, compare his work with the printed sample from which you gave the dictation. Make note of any misspelled words and discuss any punctuation errors.
I'll provide some guidelines for correcting spelling mistakes in my next post.