PS. I have a son who skipped 5th and he had no trouble academically or socially. He still was the top student. The only downside was maturing physically later than his friends, but he has survived puberty and is a strapping 14 yr old sophomore.
I have always kept my daughter in her grade level due to my concerns of puberty. This was never a problem in our last school because it was so challenging. However, the funny thing is that she ended up maturing early, even though she has a summer birthday and ended up looking physically older than she is. LOL