I happened to mention to DS5.5's teacher that he could read and do simple math during orientation. After the first week, I sent an email letting her know to let us know if there's anything we can do to keep him challenged (after she had mentioned twice in person how smart he was). It was then that SHE brought up whole grade acceleration. Granted, I had to request that DS be tested officially, but she was the one that brought it up.

We are still in the process of course, and we won't know the results for another week or so. So he may remain in K, with a teacher that will keep him challenged, or he may skip to first grade - though I don't look at it as DS skipping a grade, just beating the birthday rule. Either way, we're not pushing from our end.