DD did an IQ test at age 4.5, because we were considering application to a private gifted school. We didn't apply; and her results weren't a true measure of her capabilities, likely because she spent a good portion of the test under a table refusing to participate. At age 8 she tested PG.

She entered K at the scheduled time and actually had a lot of friends in school which is super surprising since she's also very 2E with terrible social skills. Had our school been willing to differentiate curriculum in any way at all, this could have worked out just fine.

I'm considering having DS (5 in October) tested, and I have in mind that it might be good for him to skip a grade at some point. His birthday is so near the cut-off for his grade that he'd still be close in age to the kids who are currently one grade above him.