What age to begin kindergarten?

What age to begin kindergarten?

What is the best "age" to begin kindergarten?  I know it varies from state to state.  In our state, you must be 5 on or before December 2.  I have a daughter who will be five at the end of November, just before the cut off.  We are struggling if we should send her to kindergarten this year.  It would make her one of the younger ones in her class, however, she seems more than ready, and wants to start kindergarten.  The school day is only a half day.  She is very mature in that, she can sit for long periods of time and focus, and follow instruction.  She did very well in preschool.  I can't imagine her doing another year of preschool relearning the same things and then going to kindergarten to relearn some of those things again... If she was at least five I wouldn't hesitate, its because she is four that makes me wonder.  I have a couple of friends who have held their children for whatever reason...and I wonder if that is the "norm" or if starting on time according to your district is the standard.