My DS is in Y1 and enjoys reading books in his head. He can read aloud with very good expression when he wants to but tends to mumble at other times. I think this is because he actually wants to read in his head so I have been letting him do this and then asking him questions about the story afterwards. His teacher says he must read aloud to practise his expression. At what stage will the teachers allow him to read in his head? I would find it hard to enjoy and understand a book if I had to read it aloud.
DS1 is in Year 3 and is still expected to read his school reading books out loud. If he isn't reading out loud you don't whether he can actually read all of teh words properly. It is quite easy to skip a couple of words when you are reading in your head but still understand what is happening, but that doesn't help the actual process of reading.
My DD is also in year 1 and prefers reading in her head. She reads a lot for pleasure (Rainbow Fairies, Secret Seven etc) and I know she read fast and skips words - when she does read out loud you can see her eyes are ahead of the words she is reading and she paraphrases the bits she has already taken in. DD was getting more and more reluctant, and when I raised it at a parents evening in March her teacher agreed that she didn't have to read everything out loud. So in class reading time she is allowed to read in her head for a while, and then the teacher will hear a bit read out, and chat about the story to check comprehension. However she now completely refuses to read aloud to me ('Mrs X says I don't have to...') and as she always prefers to read her own choice books at home rather than her school reading book we have got rather stuck. Especially as she has been given a much harder book to read and I know that she doesn't understand a lot of the vocab and more complex sentence structure. Sorry, rambled a bit there. Suppose I am saying that the teacher might let your DS off reading aloud but that might cause more issues.