My DS7 attends a charter prep school that goes from 6th to 12th grade. He is listed as an accelerated 6th grader. He loves it. The teachers, the classes, the students, all of it. There has been no bullying at all. The kids who are in some cases 10 years older than him treat him like one of the gang. His "house" even took him into consideration when choosing their service learning project to be sure he would be able to participate.
On the flip side, the public school that he attended last year accelerated him from 1st to 4th and it was a disaster. The fourth graders treated him like a freak and seem to delight in making him cry. He lasted three weeks before I pulled him and homeschooled the next year.
My point I guess is that it depends on many different factors. Your GS' personality, the receiving teacher, the overall attitude of everyone involved, the temperments of the kids in the fifth grade. Not only that but you really need to consider not only this move but what happens next. Is 5th grade the top of elementary where you live? If it is, then the following year he'll be moved to middle school at 8. Then you are back to the same set of questions/concerns listed above. Most importantly of all.... What does your grandson think? Does he have great friends that he would miss? Does he have the confidence to know that he belongs there even though he's young?
There are a million and one things to consider and I would think long and hard before I would give my son's schedule to anyone else. It works for him but it works because of who he is, not how old he is. If he was intimidated by older kids or the work load or anything else, it would fail in a big way. This is one of those things that truly has to be taken on a case by case basis.
