This is how I am doing studied dictation. I'm sure there are other specific ways to go about it but this is what I am doing and it has shown to be a GREAT method of improvement in my ds's reading, writing, and spelling.
I choose a passage from a book. We first began with a Bible passage, then one from his Sonlight George Washington book, and right now we are using a page from "And Then What Happened Paul Revere?". Now you must know that ds still does "Explode the Code" workbooks too, because he is a delayed reader and it is all just beginning to click. These workbooks help me too, because I can point out rules he's learning in ETC during the dictation session. So these two lessons cross over quite a bit which is helpful for ds.
I took the page of the book I wanted to use for dictation and actually just photocopied it and put the page on a clipboard. Depending on how difficult the passage, I have ds read a sentence or two or the whole paragraph. I use a highlighter to mark various words, blends, digraphs etc. With the Bible passage, it was a couple of sentences, with a reader like Paul Revere, we read the whole page. The page I chose is part picture, part text so it's not too much for him.
We read the text, then I choose three words for him to work on spelling. We were using a wipe off board and using the CM method for spelling.
The CM spelling method is simple. You just write the word out, and have the child "take a picture" of it with their eyes, give them a few seconds, I basically count one second for each letter. Then have the child close their eyes and spell the word back. Then they write it down. If they begin to make a mistake, erase it right away. CM never wants them to see the word misspelled, she wants only a picture of the correct way to impress in their minds.(This is where modern education and CM differ, at PS they are allowed to use "inventive spelling"). We do this part every day. Choosing three words a day, sometimes the same words, sometimes a few more, but only three per day to work on. I want to make sure he can spell all the words he needs to by Friday when I dictate a portion of the passage.
I mentioned that we used a white board, but beginning this week I started making an index card with each word on it with a sharpie, and I just have him spell the word with pencil/paper.
On Friday we get out a composition notebook that he writes his dictation in. I let him look at the passage once more, noting the words he worked on. Then I dictate a portion of the passage to him and he writes it (note: if there is a proper noun that I haven't had him spell, I will write that out for him to copy, CM did do this too I believe). I do not repeat, but just dictate a portion at a time. I do however still have him erase if he begins to write a word wrong, not wanting him to "see" it incorrectly.
Now some children may be able to do more than this, but as I said, he is a bit "delayed". All I can say is that since beginning this method in January, I have seen such great improvement! He even wrote his own short narration and spelled everything correctly the other day!!! I didn't think that would happen for a few years yet!
One more thing, we use the same passage for a few weeks, dictating a different sentence at the end of each week.
I have decided that for the Paul Revere passage, I am going to dictate the whole thing, doing a sentence or portion of a sentence each week until he has written the whole thing. My son is also allergic to pencils so I do have to keep the lessons short, this whole thing takes less than 20 min.
I'd like to add that we use a product from Little Giant Steps called digit span, just the other day I realized that this dictation/spelling method is similar to their neurodevelopmental programs like digit span. No wonder it is working!