i think my son has dyslexia

when he was young he had speech therapy they asked him a question and he gave a bizarre answer eg what does fed up mean ? he answered  they have eaten to much food . he used to get he and she mixed up him and her . now he is 12 yrs old and in his second year of high school his reading is only 1 yr behind but when asked to write work down he can not understand what he has written should i have him tested as he was very upset tonight and i would like to help him

[Sally44]

As you have posted in this forum I assume your son also has a diagnosis of an autistic spectrum disorder?
I understand everything you are saying because my son, who is nearly 8 is the same.  
I have been told that the difficulties could be down to problems associated with autism such as problems with visual/auditory memory retrieval.  So, it is easier for them to read than to 'access' the words that they need to express what they want to say and to put that down on paper.  So their tends to be an imbalance eg. they can read, but not write (or visa versa), and that may also show itself in their language skills ie. they may be able to speak but not understand instructions, or may understand other people but not be able to speak themselves.
As you say it might be down to dyslexia (some difficulties associated with autism and dyslexia are similar anyway).
What kind of school does your son go to?  Is it mainstream, mixed, special etc.  And are you happy with the support he gets in school and the school's attitude and approach towards your son?
I think the best way forward is to ask the school to refer him to the Educational Psychologist, although I am wondering why they haven't done so, as this is not a new problem and he is now 12.
The Educational Psychologist should be able to do some assessments to try to find out 'where' in the sequence of skills needed to read and write his difficulties lie.  Put your request in writing.
I would also recommend you contact the National Autistic Society in your own country and get some advice from their educational helpline.
From my own experience, I believe the outcome should be that they will work on the areas of difficulties he has, but that he also has access to a scribe.  This is a person who writes your work for you.  You have to tell them what to write.  There are also things like voice recognition computer programmes where you talk to the computer and it prints the words.  But as he has these difficulties the school should have ways for him to demonstrate learning other than having to write it down.  He could use tape recorders, videos etc.
Regarding the speech problems this is typically literal interpretation of language that many children/adults on the spectrum have.  There is also Semantic Pragmatic Disorder, which you may find useful.  Although he is now much better he will still have underlying language processing difficulties that will make it longer and harder for him to take in what everyone else does in seconds.  If he is better than that, and you think he has no language/communication problems that is great.
Out of interest, how did you son learn to read.  Did he learn whole words or did he learn phonics?