DS did early K. At his private school, he was switched from PreK to K midyear, just after he turned 4. He finished out that year in K and we enrolled him in K again at the public school (he has a November b-day so he was still 4 when he started.) After he turned 5, he was again accelerated midyear to 1st. There have been a few rough patches, but overall, I think the early entrance/grade skipping was our best option.