DS attends Nursery of the school which he will start in September. As my DD is in Year 3, he was already familiar with school, staff and children before starting Nursery.
It is a tiny village school with 3 composite classes, so he is in a mixed Nursery, Reception and Year 1 class. This means there is not likely to be the same need for transition as in other schools; he will be in the same class in September as he is now, with the same teaching staff and many of the same children.
He does mornings with lunch now, so he's actually there from 8:40am until 1pm and he is used to sitting in the hall and eating with the rest of the school children. That won't even be a surprise for him come September!
When he does start Reception in September, he will begin on the same hours he does now and will work up to full-time by the start of week 3; they do something like 7-8 days part-time, then straight to full-time hours.
The only thing that will be new for DS is that some days he will be on the school bus; we live in a rural location and many of the children are entitled to school transport. However, he will have his DSis there with him and I often do pick-ups and drop-offs in any case university timetable allowing.
With all the above in mind, I expect the transition to be very seamless... With the exception of the extreme tiredness that seems to hit most reception children at some point during the autumn term!