My kids go to a private bilingual school. They were 16 and 14 when we got here. We had no other choice, as I wanted to keep the option open to go back to Belgium 2 and 4 years later.
I checked the universities in Belgium where they told me they need to do their IB exams so i went looking for that. Few schools do this international IB program.
Bilingual schools do a double program, they do the national one (in Spanish) and on top of that, to get to international standards, they get more maths, science and languages.
My kids had 32h school in Belgium, in argentina they have 40 hours. (in this there are 5h of sports a week, in Belgium they had 2h a week)
So now, after 2 years, my son is turning 18 and is in his last year, finishes in december, hopefully has his IB. He is fluent english (his 3th language, but he is doing IB English first language high level, which was required), and fluent spanish (he spoke no spanish before we got here, now he does IB spanish second language high level). He will return to Belgium in february to jump in the 2nd semester in university. He is half a year behind on his Belgian friends and he hopes to catch up.
When you chose a school it is in my opinion important not to cut off/limit their future. I first looked for a school here, only after I found one that was in my opinion good enough, we decided to move here.