We did this for our kid (two grades actually). Best thing we ever did. PE is awful later on in middle and high school, but who cares, really, when they're making straight A's and enjoying the challenges in everything else?
We live in a different country and found that a byproduct of acceleration was success at sports. My daughters started school as early age entrants and physically developed alongside their older grade peers (6-18 months older), but when they competed at sports, they were placed amongst age peers and the physical difference was startling when they lined up at the starting blocks.
Academically, however, because my daughters did not perceive that they were much younger than their grade peers, they only thought of themselves as average achievers until they eventually overtook their grade peers, whereas my son stayed amongst age peers throughout his school years (no one would have considered him for early entry as he was not a well behaved, compliant three year old as my daughters were) and was far ahead in knowledge and understanding because he was a consummate self directed learner (many of his teachers admitted that he often exceeded them and allowed him to substitute activities as long as he didn’t disrupt the class). He was offered radical subject acceleration at the beginning of high school and has much greater self confidence in his abilities.
