We are in the same situation... our daughter is 4 and will be 5 in November. We could send her to K this year, but opted for an academic Jr. K program at a nearby preschool.

I initially (beginning of last school year) had thought she would do fine going to K this year, but after helping in my son's K class, I started to see how the children (especially the girls) interacted with one another and how quickly things got quite competetive. It was a real eye-opener and made us decide that giving our daughter another year of childhood would be a good thing.

I see my teenaged daughter (who is now 15 and a sophomore) having to make tough choices many times, and it makes me even more glad that we are deciding to hold the little one back a year. Knowing that she will have another year of critical thinking and decision-making skills under her belt when she has to face peer-pressure stuff is a good thing, imho.