My girls went/go to a IB K-8th Charter school. It was an "international school" and then had to jump through a bunch of hoops to become an official IB school.
It's a challenging curriculum and a really great school. It's weird you're asking this because just yesterday I was explaining to my youngest that our school isn't the best for kids who have learning differences. As others have mentioned it's a tough program and being a charter we cannot offer the same help for kids with disabilities or learning issues that a regular public school can.
I do know that our school seems to hold kids back in order to help them get their studies on track. Being a small and supportive community it seems to not be as big a deal as it might in a regular school. I've seen a couple of kids thrive after repeating a grade.
Factors like the age of your child, his/her actual learning issues and temperament are really important factors. You can PM me if you have any questions. Good luck!