Telling your child about their diagnosis

I just wondered what others think about telling their child about their diagnosis and what's the best to do it.

My son was diagnosed with aspergers in July, he's been asking why he's different for a while. We haven't told him yet as I'm not sure what's the best way to go about it. i want him to see it as a positive not negative. also I don't wanting him using it as an excuse.

The clinical psychologist has said they would sit down with him either whilst I tell him and explain in a bit more detail.

How much should we tell him. i'm only just begining to get my head around it.

Thanks for any advice.