Update: DS is enjoying his time in 2nd grade
We didn't make a big deal out of telling him he was being accelerated just brought it up throughout the weekend. He had some moments of apprehension and would ask questions allowing us the oppurtunity to reassure him. He was most apprehensive about his age in relation to the new grade. Saying things like "You have to be X age to be in X grade." bringing up different grades and their corresponding ages at various times. As long as we worked out the math portion and showed him he wasn't that much younger then his new peers it alleviated the fears. We also gave examples of children he knew that were already in that grade (if not the same school) as him. A cousin, a soccer teammate, etc.
He likes structure in his day as far as a schedule, so we gave him his exact schedule for the day. At this time this happens at that time that happens. His first day he went to school with only a tinge of trepidation that I could tell and from all accounts things have transitioned well.
Allowing him to acclimate these last weeks to second grade has been helpful. We are glad the GATE coordinator suggested it and they followed through. Since he is also starting the day with his 1st grade peers and eating lunch with them, he has the best of both world's. When we ask about the academics and what they are working on he talks about the subjects and the books he has been given where before he didn't want to talk about it. His academic confidance is coming back.
He is asking random questions and showing interest in figuring things out on his own. We realized he was just coasting before but seeing the spark come back in his eye really emphasizes how much he needed this. He is laughing again and his obstinance has taken a back seat for the moment.