We don't have experience with a double-grade skip, but if you're wondering *where* gaps might show up, you can probably find your school districts curriculum listed by grade and subject online, and a quick glance through that might give you a good idea of where gaps *might* show up - and I'm guessing at this age that just a tiny bit of tutoring at home to fill in would be all you'd need to get past the most obvious things that might crop up.

Best wishes,

polarbear