Hi CK27, Welcome! What grade is your DS in? You can look up his scores on the charts in Appendix B here:
NWEA MAP normsAs for whether those scores are in the gifted range, that varies by district (and whether they have a gifted program at all). E.g., some districts say that anyone scoring in the 95 percentile or above is gifted, but I wouldn't say there's a standard anywhere.
You ask about grade skip versus differentiated learning. You really don't give enough info for anyone to comment on specifics. Is your DS consistently underchallenged in school? Is anyone in his grade scoring similarly? Is the differentiation working?