Just wanting to get other people's perspectives on this...
DS just turned 3 in August, he will be the youngest in his year when he starts school. He has been at a private nursery 3 days a week since he was 1. We have been very happy with the nursery, and he has been happy there. He has been loving nursery so much recently, and in particular has started making friends in the last few months.
However, most of his cohort have now moved up to the preschool room, and have been replaced by younger children from the room below. They have been moved gradually over the summer in groups of 2s or 3s. DS apparently will not move until after Christmas. The nursery staff told me this is because he is happy where he is and it will give him the opportunity to be the oldest in the room for a bit and lead play. Out of his original cohort, there is just him and 2 others still remaining in the current room (out of about 20), and at least one of them will move in October.
The thing is, he now seems a bit subdued, less eager to go to nursery. Today he told me he missed his friends and that he hadn't had a good day. One of the nursery staff told me he had had a good day, but was missing his friends and bit and occasionally was wandering around on his own looking a bit lost. I'm ok on him missing out on the educational side of preschool, but I feel sad that his social circle has been broken up. The cynical side of me wonders if their reasoning for leaving him in the younger room is just an excuse? Especially given that several other summer born children have already moved up. And perhaps the real reason is that staff:children ratios make it more economical for them to hold a couple of children back?