My kids do that
(They're homeschooled)
Seriously though, I think it could be really good or really bad. If he and the teacher don't get along well it wouldn't be good to be stuck for 2 years. Also, if there were problems with some of the other children it could be bad. On the other hand, it would make for less of an adjustment period for starting second grade. And, I would think that probably this opportunity would be given to the better teachers first.
I went to a really small school for K-8th so it was practically like that the whole time. I had the same teacher for 4th and 6th grade. From 4th - 8th I had a lot of the same teachers every year for different classes. It was a good experience overall.
