I felt the same way as you do with my DS1. He seemed soo small and the schools seemed so big. So I kept him in nursery an extra year. But in retrospect, schools are pretty much the same as nurseries at that age. And it was much harder to get him into a school at 4. Having said that, I would be more concerned about the ages of the other students in your DD's class. Are they all just turning three or are most of them closer to 4?