If schools are all teaching to similar standards, then students can transfer between those schools without skipping a beat. That's kind of the point when it comes to any national standards we have. We assume that a 10th grade English, chemistry, or trigonometry class hits all the same marks. AICE requires similar standards at all of its partner schools, which means that the main challenge of a semester exchange would fall with non-AICE classes. I know it might mess up some student GPA dreams, but non-AICE classes would just have to apply to general electives. Stuff like art or gym. Maybe a study hall.
I'm not sure about AICE semester vs full-year classes, but I'd think second semester would work best for an exchange: students would have a semester with their home-area teacher and then get additional guidance from an exchange teacher, having access to resources from both instructors for what should be a very similar test.
It's likely schools participating in the exchange could be privy to the differences in expectations and adjust to the class that's being taught and students involved. Even if it's only a few schools that offer this, it should work. For example, Fletcher High School in Jacksonville could prepare AICE teachers to teach Americans and British kids, (allowing some Brits to get a little sun and beach time in their lives).
I guess I'm disappointed that an AICE exchange program was never really a thing, leaving Amity and other programs to do whatever they do. Honestly, even if it was just a two-week exchange, I'd still be happy to have my kids participate. But since the idea wasn't really a part of the AICE philosophy from the start, it's probably not going to happen, unless enough AICE parents and students read and share this post and call for some kind of in-person exchange. It's really kind of the point of an international curriculum.