One caution is that this can lead the child to assume that this is a TRUE 'weakness' or area of struggle, since they don't have an accurate frame of reference.
Yes, this has come up with math this year. DS9 is effectively grade-skipped twice (one skip in the regular local school, and then a transfer to a school for HG kids that is accelerated at least a year). He started saying that he's no good at math (mostly because he's not at the top of the class). It helped to show him the the chart depicting where his scores are compared with the rest of the district (not just his class). This helped more than reminding him that he's at a year younger than most his classmates, that he's still in the 99th percentile, that scores go up and down, etc.
Believe it or not, most of the time, after the FIRST skip goes well, the school becomes more willing to consider doing it again if it seems necessary.
The held true for us. When DS skipped 1st grade and was still underchallenged so we were trying to find solutions, I remember the principal commenting more than once that she forgot that he had already skipped a grade. Once the school sees how successful a grade skip has been, things get better. They must see for themselves that their long-held beliefs (skips are not a good idea) are not true for everyone.
