Welcome, beak!
I'm not familiar with California at all, but I had a few initial thoughts when reading your post.
First, in my experience, preschool teachers very often tend to err on the side of caution and recommend extra time in preschool and K, especially for boys, so if your son's teacher is recomending that your child needs more, then that says a ton to me. I would definitely use this teacher as a resource, a source of support, and as an advocate for your son. Would she be willing to call schools that are options for you to say, "I have this student in my class that I feel very strongly is ready for a 1st grade classroom . . . " and see what she gets? Sometimes an educator to educator conversation is very helpful. If not a conversation, would she be willing to write a letter of recommendation detailing specifically why she thinks 1st would be a good placement?
I thought it was interesting that you said the school system's web site discourages trying to get around this deadline. To me, this sounds like a door is open for someone for whom getting around the deadline would be truly appropriate.
I think the idea of your son staying where he is for another year and then entering into 2nd grade is an option worth looking into. If he's in an nurturing environment and they are willing to provide the level of learning that he needs, it may make the case more obvious to the other school that he's beyond their curricula.
I have heard of a few rare cases where schools do not require testing when looking at grade or subject acceleration, but virtually all do. They want something "tangible" that shows them that not only is the child ahead now (which could be due to you being an attentive parent, they think) but that your child is highly likely to continue to learn at a much faster pace than his peers. So, in conjunction with you looking into his schooling options, I would look into testing options, as well. I know that when we were looking at early entrance/skipping K, the school provided us with a free individual ability and achievement assessments as part of their decision making process. For others, I know it's sometimes necessary to get the assessments yourself, but in that case it would be helpful to know which tests the schools like to see.
Another thought: what we found very valuable, and what the school found very valuable, was having a day where our child visited the classroom into which he or she would be placed the following year to see how they did with peer interactions, self-starting, separation, academics, etc. In our case, our kids visited a K class for several hours to see if they would be ready for K the following year. The thought, I guess, was that if they could get along well in the K class at that point, then they would certainly be ready for K the following year. Perhaps your son could sit in on a 1st grade class for a day this spring, or could sit in on a K class which would hold the kids who would be his classmates in a 1st grade class.
Good luck beginning your search for school options. It will become an obsession at times, but *try* not to let it take over too much of your time. It sounds like you've got a great little guy!
