When my oldest was transitioning from elementary to middle school, we got together with the middle school to arrange time for a tour- before the end of the current school year. So he could see the amount of kids were moving around, the noises and smells that went on. It was a bit overwhelming, but it helped a lot. We met with the department head of the special education so she had a name with a face, because of his anxiety, I knew she would be working with him a lot. We also drove around the school periodically during the summer so by the time school was in session, it was great. Also, something to think about, if he's going to take the bus- 2 things,
1) Be sure someone takes him to his bus stop on the first couple of days so he doesn't go on the wrong one.
2) Look up the bus route on line and drive to the map= let him see how the route would be and so he knows when to get off the bus. Hope this helps :)