NAEYC says redshirting is overall a bad idea for kids (http://journal.naeyc.org/btj/200309/DelayingKEntry.pdf ).

And this study shows no social differences by the end of first grade. http://ceep.crc.uiuc.edu/eecearchive/digests/ej-cite/ej516737.html

Everything depends on your local circumstances; look closely before you decide.

DeeDee