Learningmom, I am especially concerned about the apparent contradiction in:
"Psych hadn't received the report from his teacher but told me that he didn't see Asperger's or LD. ... I received the written report yesterday, and it was completely different. He diagnosed mild PDD-NOS and possible dysgraphia. The report said that the teacher eval coincided with behaviors that the tester observed as well, but that we don't see at home near as much."
If you can possibly have your child evaluated somewhere specializing in autism/PDD to get their expert opinion, I would do so. My oldest child was born with autism, and you would be surprised at all the contradictory diagnoses we received (and he DOES have the diagnosis). My son really does have autism (looks more like Aspergers now), but I can tell you these disorders on the autism spectrum are not well understood. I would not place too much confidence in any one opinion, ESPECIALLY given what you described (apparent flip-flop after getting the teacher's report). ONE teacher thinking a kid is on the autism spectrum might mean only that the ONE teacher did not connect well with your child. I have never heard of a child anywhere on the autism spectrum who does not exhibit many signs of it in most settings.
If this psych really thinks your child is on the autism spectrum (even if mildly so), I'm surprised there seems to be no mention of any interventions recommended outside school, or perhaps a call for further investigation at a center for autism (so you as a parent can get appropriate direction)? Maybe you live too far away from an academic center like that (where there would be an autism specialty program). Without a more thorough workup by people who really know autism in all its variations (even so-called "mild" PDD-NOS) I would doubt this diagnosis.
If I were you I might be tempted to try an "experiment": since you are now homeschooling (great choice, and your child is lucky by the way!), maybe you can send something in writing to this psych (friendly tone of course) and say you are concerned since your child now has this autism spectrum diagnosis and you are homeschooling, you are looking for some expert direction on helping your child as much as possible. You could ask for more specifics on what led the doctor to diagnose the PDD-NOS (never mind the "mild" since I think officially diagnoses don't come as "mild" or "severe" but are just there or not there). Tell the psych you are following up at an academic center specializing in autism (maybe UCSF Langley Porter Psychiatric Institute?) or if you know another highly regarded one close to you, maybe name that one? I wonder how this psych will respond. I wonder if the response will in any way show the level of confidence (or lack of it) this person has in having applied that diagnosis with your child. The response might also reveal something about this psychologist's familiarity with such centers (who knows, maybe he worked at one?) Alternatively, we may discover this psychologist is not terribly familiar with autism in all its manifestations. PDD-NOS is a serious diagnosis, and I think it is reasonable for you to take it very seriously, and follow up accordingly. Good luck.