My two cents: While acceleration may not be the ideal solution, the cost of NOT accelerating may present more negatives, such as:
- lack of challenge leading to boredom,
- loss of sense of discovery, exploration, curiosity,
- development of an unwillingness to struggle and risk making mistakes,
- dearth of opportunities to learn from one's mistakes/failures,
- failure to develop perseverance and resilience,
- lack of respect for other people and their struggles/failures.
- More at this post.

Adding a link to a thread called what kids don't learn, which contains an article listing 10 essential skills which are developed through effort, such as experiencing appropriate academic & intellectual challenge... skills which people may not develop without this level of challenge.

A single-subject acceleration (such as math) affords the child the opportunity to be with academic/intellectual peers for math while also spending some time with chronological age peers for other subjects.

Here are some links to old forum discussions which may be of interest:
1. Thread called Polling Davidson forum members on acceleration, which discusses whole-grade acceleration (grade skip) and has many links to other threads with thoughtful responses on children's experiences with having older friends/peers/classmates. A list of these links is also summarized in this post from a thread called Considering a grade skip.
2. Post linking to "The Right Fit" authored by Tamara Fisher, from archives of her column Unwrapping the Gifted, for Education Week.

Bottom line: Think in terms of matching the program to the child, rather than matching the child to the program. Take each year at a time, and adjust as needed to facilitate your unique child's academic, intellectual, social, and emotional growth and well-being.

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NOTE: In the first paragraph above, the article linked to the text "learn from one's mistakes/failures" is titled "Tips for Parents: Preparing your Gifted Child to Leave Your Nest and Build Their Own," by Steve and Tonya Witherspoon (2012). It is archived on the WayBack Machine, and to find it you may cut/paste this link - https://web.archive.org/web/20151029080359/http://www.davidsongifted.org/db/Articles_id_10761.aspx