Hi K.,
I have recently been in your shoes! My son is 6 and in the 1st grade. We just moved here from Germany in November and my son has had a good/bad experience with him. We talked for a long time about how we were going to be moving and all the fun things that we would do at our new place and how much more we'd be getting to see our families. (We're Air Force, originally from South Dakota so now we can see family more often than we have in the last 6 yrs.) We also let him use our camera to take pictures of his favorite things around our house, the area we lived in, his friends, you name it.
The key is to talk positively about the move, talk about the fun things you can do together to his new room, and how fun it will be to meet new friends and see the new things.
Is it possible to visit the new town and school before you move so he can see where he will be going? That may help relieve some of his anxiety.
Now I will say this, my kiddo is very sensitive and we are still having trouble with him missing Germany and all his friends there. I allow him to email his previous teacher and class, it lets him keep touch with something there and share his fun experiences here. Crying and being upset is not unusual - and it's actually good for them to miss people. Although it is heart wrenching to go through when nothing you do or say seems to make them feel better!
Good luck to you!! :)