I agree to go with their interests. I have a son on the autistic spectrum. He can immediately memorise his reading book, but cannot actually read yet. He is 7.5 years old. He loves TV/DVDs and recently he has been learning Greek from watching DVDs sent from Greece (my husband is Greek). So he has begun to tell me what certain phrases in Greek mean!
I think that along with autism, children with ADHD and dyslexia etc find the way that reading/writing is taught today difficult to access. For some reason phonics was introduced to supposedly help those with reading writing problems, yet those with those problems tend not to learn through phonetics!!
I too have been told to encourage reading by choosing a book he is interested in, and then reading the parts that he cannot read and encouraging him to read what he recognises, even if it is only one word out of the whole page.
An Educational Psychologist should have some ideas as to other approaches or strategies or reading programmes to use. If your son has ADHD and has an IEP then raise these concerns in writing.
You need to find stories of high interest for him - maybe junior novelizations of movies. The problem with most readers is that they are not designed for high interest for a child of his age group.
I think Options Publishing has a series designed to help struggling readers but the books aren't too babyish.
I remember when I taught my kids how to read I read a page and then my on read a page.
There are a lot of great kid magazines where the stories are both short and of high interest - like Discovery Kids. My son gets several of those (to be far - though he goes to a school especially designed for ADHD kids - reading was never a problem) and he likes them. Lots of pictures and cool stories.
If he is willing to listen to you read - which also builds vocabularly - look into the Percy Jackson series - a re-imagining of the Greek myths in modern day times - where the hero has ADHD and dyslexia.