With a kid this age, it takes his buy-in, as well as a very clear understanding of what problems are to be worked on and how. We work on goals over the summer (we work on goals all the time, it feels like), but we try to make those goals harmonize with DS's projects and plans rather than making them an extra time commitment.
If writing is a problem area, I'd want to make sure it gets into the IEP as a priority during the school year (with lots of detail about what the present level of achievement is for different kinds of writing, and what skills are missing). Often taking family out of the equation of writing instruction helps.
I wouldn't attack writing while you are also prioritizing working on social perception, and while he's probably going to be working to accept new diagnostic information about himself. He will need some time to just be, and not to be pushed to remediate his deficits all at once. Nobody likes feeling like they are someone's project.
