Have you looked at the Iowa Acceleration Scale (IAS)? It provides sound guidance for thinking through a number of issues/aspects which parents/child/teachers may not have otherwise reflected upon.

Familiar with up to 4 years of successful acceleration, while there is good and bad in everything, we have found the benefits to far outweigh the drawbacks.

Whichever choice a family makes...
"Things work out the best for those who make the best of the way things work out." - John Wooden