Our daughter is an early August birthday, and she is just about to leave primary school.
My overwhelming experience is that these children are very much treated as the 'babies' of the year, both by their peers and their teachers.
In some respects I could see the logic, as it was obvious that in some areas of speech and physical development, I could see the older kids in the class had already reached a certain stage in development.
It frustrated me terribly, as I blamed myself for not holding our daughter back one year, so she would be one of the oldest in the next year. Sadly that option wasn't available to us 7 years ago. I understand it is now.
Having sat on my school PTA for 7 years, and getting to know teachers on a first name basis, rather than just as a parent, some teachers even admitted that they sometimes overlooked the younger, less developed children.
What I would advise though, is to prompt teachers at every stage of Primary to include your child in every event, every topic the class offers, and if this doesn't work, and you can afford it, hire a tutor.
Ask the teacher/s to provide you with course work if they are willing. to.
Again frustratingly, some of our teachers would not provide the course work.