So, this is from the perspective of having done K with my oldest and preparing for K with my youngest. DD did indeed have lots of those basic K milestones mastered at 3 or 4. However, she would not have been capable of the level of maturity, regimentation, penmanship, and direction-following that now characterize K--at all. She was far ahead, of course, starting the year reading at somewhere above the 3rd-grade level. And DS is going to be far ahead, too. However, he absolutely could not handle K now, regardless of the actual skills, such as counting to 100, basic reading, basic math, colors, shapes, and so on. That stuff is part of it, buy by no means is it the whole enchilada.
It doesn't mean it's going to be a good match for my son--it probably isn't. It wasn't great for my daughter. However, she wasn't as far ahead, in terms of how the day was actually spent, as those milestone lists might make you think. And it doesn't mean either one was a good candidate for early entrance or skipping.
