DS7, at 5, made those small revisions while reading his home reading books (from school) aloud. It took me a few examples to realize he was correcting grammar, syntax or improving the fluidity of the text. Once I clued in, the next time it happened I told him that his revision was correct and that I was impressed he caught the mistake. Then I explained that even if the text could benefit from improvements, he still had to read it the way it was written for his teachers. Which left him both pleased with himself and reasonably happy to comply. Plus now he revels in catching me in the same revisions!
I think fluent readers do this instinctively - including in their heads while reading silently. I was actually delighted when I realized what DS was doing (after I made him read the text as written and saw that he could, of course!).
