Let me say what a childhood as an army brat did to my education. 10 primary schools and 21 permanent addresses by my 21 birthday.
I only went to two secondary schools. because I went to boarding school at 12. If I hadn't I would have had three more changes of school in my secondary years including the final move in the Easter before I was due to take my A levels, where the chances of finding a school doing exactly the same syllabus as my previous school in the new area, would have been nil, assuming it was not too late to enter the exams. i could not stay in my previous school because it was in Malaysia, where I had no family or very close friends and my father was moving to Germany.
Boarding fees were available to all ranks and we had girls at school with me whose parents were not officers. The reason more children from the lower ranks did not go to boarding school was the result of their parents decision to keep them with the family.
I appreciate that much has changed but remember these rules were drawn up when people moved much more.
I taught children of army officers based in UK when they were in primary school. They went off to boarding school around about 9 even though their parents were still in the UK. This is a sweeping generalisation, a number do, but many do not.
When parents are looking ahead to a career of house moves, often at short notice. It makes sense to plan ahead for your children's education.