Autism screening tests for older children - how reliable?

[MGMidget]

My DS has seen a paediatrician (NHS) for ADHD and was found to meet the criteria for ADD. Paed referred for a number of other tests and experts to see DS, including a referral to CAMHS for autism assessment. I filled out another questionnaire for this and so did the school. My questionnaire was the SCQ Lifetime questionnaire. I found it very difficult to answer all the questions reliably as approximately half the questions related to specific behaviours between the ages of 4 and 5. My DS is 9 so this was half his lifetime ago. I noted in several places on this questionnaire that I found it difficult to remember as it was so long ago - however, I took a guess at every answer.

The next step was I was that I had a call with a clinical psycologist to go through the results. They informed me that my son scored 10 on the SCQ Lifetime questionnaire and hence didn't meet the 'cut off' of 15 to qualify for an autism assessment. After talking through his behaviour and school report with the psycologist, they concluded that DS did have some problems with social communication and some ASD traits but not enough to qualify for assessment as he didn't meet the cut off on the SCQ questionnaire. I was advised that I would need to help him with developing his social skills and accept that he would be slower than his peers for the rest of his life at certain things.

Part of me is relieved that he doesn't seem to have ASD. However, I had started reading up on this in preparation for the assessment and my DS seems to fit so much the profile of high functioning autism that I am puzzled that he has been dismissed from assessment so readily. Therefore, I tried doing the CAST questionnaire which screens for Aspergers and my son scored 21 which would seem to indicate he fits the profile for Aspergers.

I wondered therefore, how reliable Is CAMHS for assessing autism and how reliable is the SCQ Lifetime questionnaire for assessing older children for autism? I found it so hard to remember and answer the questions on his behaviour between ages 4 and 5 that I wonder how this can be relied on as a means of deciding who does and doesn't get assessed for ASD!