Just to add, I also see lower/average WM scores in gifted kids who are not necessarily highly motivated in tasks that require lots of mental energy (because they like things that come easily). It takes A LOT of mental energy to remember number sequences, and letter-number sequences. Do you have a digits forward vs. digits backward subscore?

This is also true of kids with ADHD- so it is good to figure out if it is just motivation or is it ADHD.