Our state tests against end-of-year-to-be-skipped standards, and requires a 90% pass rate.
DD barely squeaked by the 90% cutoff. A month later, all the kids in her post-skip grade were pretested against end-of-grade standards, and she was hugely ahead of average. The 90% standard, IMHO, is too high. Even with that, there were things that the other kids had seen before, that DD hadn't.
I personally wouldn't worry about identifying gaps before the skip. If something comes up that's an issue, she'll either pick it up, or you can teach it briefly at home, or the teacher will cover it in the review that at least one other kid in that class is going to need anyhow. There just isn't that much stuff that gets learned in first grade.
