Even if you're right and readiness is there, the sooner you introduce formal instruction, the sooner the gap widens to the point that you begin to be pressured to find an alternative when your child outstrips the rate/content faster than peers (even those older).
I agree completely! We're running into that now!
With Montessori, you might be OK with this, but we are struggling right now because my daughter's Pre-K program put her in a year early (we came up with another plan to keep her on par with her age group, but her school couldn't keep up & accelerated her). Now, we need to figure out next year... she graduates her pre-K this year (with pretty much no asynchrony -- she's even the size of the other kids!) with pretty much no option for next year.
Public has a strict no early entry policy (even in charters), so we've had to go the private route, which still involves evaluations and paperwork, etc. So, if you can avoid acceleration until they are at least old enough to be in the "public system" you might be in a better place.
Personally, we have our little girl mostly play oriented with a single instructional class (she takes Ballet) at this age (3.9) and she is thriving. Best of luck on your decision making process!
