It is common to have high funtioning disorders diagnosed at age 10 or later, and it would not be uncommon to have met all the developmental milestones on time and still have an ASD, however, it might be a little uncommon to have few social issues prior to 1st grade, but not out of the question. You should know that there are many different things this could be that are not on the Autistic spectrum. The one that comes to my mind is NVLD, which presents with overlap of both ASD's and ADHD, but has a distinctive LD component in Math.
I would suggest that you invest in a private evalauation right away. Since you need one quickly, I suggest that you consult a board certified Child Psychiatrist and ask for a referal to a Neuropsychologist for an educational-psychological evaluation. If you do not get treament from a psychiatrist for the ADHD, I would switch now. If you have time to wait it out over the summer, you might also invest in an evaluation from a Developmental Pediatrician, through the developmental pediatric offices at your nearest children's hospital. This may take several months, but it will give you the gold standard for developmental evaluations. What ever he needs (from geneticists, to OT's) will be called in, and you will not wonder if you missed anything ever again. In your situation, I think I would schedule both with a Nueropsychologist and a Developmental Pediatrician and do both. Use this evaluation data to keep the school honest. The school is only required to make your son functional, and you will want to supplement what they provide so that he can truly reach his potiential.
Unfortunately, you have already held him back a year, which puts him at an educational disadvantage, and he would have come to this point last year had you not been convinced to do so. You have to move on from here, but you should be aware that every test you read is compaired to his grade level peers for purposes of school, but to his age level peers for purposes of development. Go to www.wrightslaw.com and read "Understanding Tests and Measurements for Parents and Advocates" you may need to read this many times before you understand it, but it is imperative that you do before any of the new evaluation data comes in.
I can help more as you go through this process. I have two kids on the spectrum, and the oldest is an adult. I became an educational advocate out of necessity, and now I help parents navigate the system. If you need more than general advice, check the yellow pages at Wrightslaw.com for California, and find an advocate in your area who is also familiar with California law.
Beware, if the school is evaluating for Autism, they have good reason to do so, but it may have more to do with the program they already have in mind than it does with what they see in your son. In general, they only evaluate kids for things they are willing to serve, so you are probably in for an evalaution that finds your child to be autistic. I would make it my highest priority to get my own evaluation done first, one that I owned, and one that contained a medical diagnosis that I found comprehensive and trustworthy (even if you don't like it) know for sure that you have, and own the evaluation that holds his diagnosis.
Let me know if I can help any more, get the private evals ASAP.
M.
Just a couple of things; while I suspect that the diagnosis the school will come up with may be Asperger Syndrome, it could also be PDD-NOS, generally Asperger is the highest functioning form of ASD, while PDD-NOS is more of an "umbrella" as someone said below. Because of his math issues, PDD-NOS may be a more likely finding. Also, once a child qualifies for IDEA, he is to be served according to his educational need, regardless of what category he is identifed in. Services are delivered based on need, not diagnosis. This is the proceedural nature of IDEA, and you will need to understand it fully to get your son what he needs. Avoid any "blanket" ideas that make any of this sound simple, it is not that simple; it is extreemly complicated and that is why you need to learn which of the statements below are far too simplified, and dreadfully innacurate because they will cause your son harm if you don't know what your are doing here. I don't say that to scare you, but you should be ready for a process that will not be at all fun, it may be confrentaitional, and it will be more so if you do not educate yourself before hand. After skimming a few of the responses, I just want you to be very careful, and get as much help understanding IDEA, ASD (and possibly NVLD) and evaluation data as possible so that you do get exactly what your son needs.