This is one of the main reasons we pursued a skip for dd14. (She skipped 6th) There were many tears over math for a short time because she wasn't used to understanding immediately, but she learned to struggle (a little) and that it was ok to not understand right away. The greater challenge really served her well, and I can't remember the last time she cried about math. We wouldn't have been confident asking for a skip without the private testing that showed it was warranted.