'should you be in Brussels like Scary, there is school funded by all the Member States, also open - gratis - to children of diplomats of the EU member states and NATO serving military staff'
It is NOT open to NATO serving military staff - NATO come bottom of the pecking order to get your kids in - been there, done that. The Fonctionnaires at the EU can get their kids in, but if like us, you are NATO, then EU, and then back to NATO, we would have had to move ds three times, and that is not continuity of education. Ergo, he goes to BSB, where he has continuity.
There is no room at the EU schools, they are overcrowded, and certainly for all the Brit mil kids here it is BSB or boarding in the UK. BSB mainly because it offers GCSEs, and that is what most of them would do if they went back. Where we are in the UK normally, no-one does IB, which is why we went to BSB.
The other problem is the notice you get to move with HM Forces. I think we are staying here for another 3 years, but between now and when dh is due to move appointments that could change and we could be sent back to UK. You can't just 'slot in' to comp; it depends where you are sent, what GCSE courses they do if your child is in Year 10; do they match what they were doing previously?; what space is available; do you have to go to appeal to get them in to a good one, or do you just send them to the one with 29% A*-C passes down the road. If you don't have your own home, and the Married Quarter people won't give you an address, you can't apply for a school place until you have an address, ad sometimes you only get that two weeks in advance. It is because the process for getting a school place in the state system is so awful, that we have Continuity of Education allowance to avoid that; or one spends potentially years living apart from your spouse in order to have your child educated locally.