If he's a visual learner, I'd do what shiremummy is suggesting and create a social story. Take some photos of the two different routes to the two different schools, pics of the schools and teacher (if possible). If there's anything he's particularly anxious about try to ease those concerns. And talk, talk, talk about all the good things he's going to do at the two different schools. I'd try to use the schools' different names so he can start to differentiate, and if he needs to wear a different uniform to each, perhaps get him to test run the uniform on the appropriate days during the last few weeks of holidays?

Depending on his needs, it may suit him to have two sets of things - one for each school. eg two backpacks, two lunchboxes etc. Or it may be good for him to have one continuous thing across the whole week, iykwim.

Also, depending on your child, you might wish to arrange to ride the bus with him during the first week (but this could backfire on you and he may associate you with the bus and expect you to be on the bus all the time).

The good thing is that you already know him very well You know what he'll respond to best in terms of preparing him. Whatever works when you prepare him for a new experience now, will most likely be the best option for preparing him for his schooling. All the best.