school?

we thought we had it all figured out. then, more questions seem to arise each day.
i was stopped today on my way out the door after dropping levi off at school. his teacher wanted to "chat" about levi's progress and plans for next year.
we had decided, after much debate, to hold levi back one year instead of starting him in kindergarten. to give him a leg up when he finally starts, being the oldest in his class instead of the youngest. and we all think this decision will be the best one for him.
so, when the teacher approached me today, it was to tell me that in the last month, levi has been making leaps and bounds in his progress. he is becoming much more proficient at writing his letters, he is starting to sound things out, he is expressing his feelings with words instead of keeping them inside, and he is starting to really engage in cooperative play and imaginative play. she wanted to tell me that he really is loving learning and has finally opened up to her and is an absolute sponge when it comes to education.
its not to say he is ready for kindergarten- she also agrees one more year of preschool would be worth it. but, it is to say that she wants to be his teacher again next year.
we had thought, if we were going to keep him in preschool one more year, that we would move him to a different environment. its not that we dont love levi's school- we do. but three years was enough and we we not sure a fourth year would do any good. but his teacher (and the head of the school, who was overhearing this conversation) said that moving him for one year would be detrimental to his education. he is finally comfortable, learning well, that having him make a huge transition for one year, only to move him AGAIN for kindergarten, would really push back that progress.
it got me thinking. are they right? should we keep levi in his current school for one more year? should we move him to a different school for pre-k only, increasing the transition time twice instead of just once? what should we do. i need some advice.